PM> Install-Package Spire.PDF 

using Spire.Pdf;
    using System.Drawing;
    
    namespace AddImageWatermark
    {
        class Program
        {
            static void Main(string[] args)
            {
                //Create a PdfDocument object
                PdfDocument document = new PdfDocument();
    
                //Load a sample PDF document
                document.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.pdf");
    
                //Load an image
                Image image = Image.FromFile(@"C:\Users\Administrator\Desktop\logo.png");
    
                //Get the image width and height
                int imgWidth = image.Width;
                int imgHeight = image.Height;
    
                //Loop through the pages
                for (int i = 0; i < document.Pages.Count; i++)
                {
                    //Get the page width and height
                    float pageWidth = document.Pages[i].ActualSize.Width;
                    float pageHeight = document.Pages[i].ActualSize.Height;
    
                    //Set the background opacity
                    document.Pages[i].BackgroudOpacity = 0.3f;
    
                    //Set the background image of current page
                    document.Pages[i].BackgroundImage = image;
    
                    //Position the background image at the center of the page
                    Rectangle rect = new Rectangle((int)(pageWidth - imgWidth) / 2, (int)(pageHeight - imgHeight) / 2, imgWidth, imgHeight);
                    document.Pages[i].BackgroundRegion = rect;
                }
    
                //Save the document to file
                document.SaveToFile("AddImageWatermark.pdf");
                document.Close();
            }
        }
    }

Imports Spire.Pdf
    Imports System.Drawing
    
    Namespace AddImageWatermark
        Class Program
            Shared  Sub Main(ByVal args() As String)
                'Create a PdfDocument object
                Dim document As PdfDocument =  New PdfDocument()
    
                'Load a sample PDF document
                document.LoadFromFile("C:\Users\Administrator\Desktop\sample.pdf")
    
                'Load an image
                Dim image As Image =  Image.FromFile("C:\Users\Administrator\Desktop\logo.png")
    
                'Get the image width and height
                Dim imgWidth As Integer =  image.Width
                Dim imgHeight As Integer =  image.Height
    
                'Loop through the pages
                Dim i As Integer
                For  i = 0 To  document.Pages.Count- 1  Step  i + 1
                    'Get the page width and height
                    Dim pageWidth As single =  document.Pages(i).ActualSize.Width
                    Dim pageHeight As single =  document.Pages(i).ActualSize.Height
    
                    'Set the background opacity
                    document.Pages(i).BackgroudOpacity = 0.3f
    
                    'Set the background image of current page
                    document.Pages(i).BackgroundImage = image
    
                    'Position the background image at the center of the page
                    Dim rect As Rectangle =  New Rectangle(CType((pageWidth - imgWidth) / 2,(Integer)(pageHeight - imgHeight) / 2,imgWidth,imgHeight, Integer))
                    document.Pages(i).BackgroundRegion = rect
                Next
    
                'Save the document to file
                document.SaveToFile("AddImageWatermark.pdf")
                document.Close()
            End Sub
        End Class
    End Namespace

PM> Install-Package Spire.PDF 

using Spire.Pdf;
    using System.Drawing;
    
    namespace AddImageWatermark
    {
        class Program
        {
            static void Main(string[] args)
            {
                //Create a PdfDocument object
                PdfDocument document = new PdfDocument();
    
                //Load a sample PDF document
                document.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.pdf");
    
                //Load an image
                Image image = Image.FromFile(@"C:\Users\Administrator\Desktop\logo.png");
    
                //Get the image width and height
                int imgWidth = image.Width;
                int imgHeight = image.Height;
    
                //Loop through the pages
                for (int i = 0; i < document.Pages.Count; i++)
                {
                    //Get the page width and height
                    float pageWidth = document.Pages[i].ActualSize.Width;
                    float pageHeight = document.Pages[i].ActualSize.Height;
    
                    //Set the background opacity
                    document.Pages[i].BackgroudOpacity = 0.3f;
    
                    //Set the background image of current page
                    document.Pages[i].BackgroundImage = image;
    
                    //Position the background image at the center of the page
                    Rectangle rect = new Rectangle((int)(pageWidth - imgWidth) / 2, (int)(pageHeight - imgHeight) / 2, imgWidth, imgHeight);
                    document.Pages[i].BackgroundRegion = rect;
                }
    
                //Save the document to file
                document.SaveToFile("AddImageWatermark.pdf");
                document.Close();
            }
        }
    }

Imports Spire.Pdf
    Imports System.Drawing
    
    Namespace AddImageWatermark
        Class Program
            Shared  Sub Main(ByVal args() As String)
                'Create a PdfDocument object
                Dim document As PdfDocument =  New PdfDocument()
    
                'Load a sample PDF document
                document.LoadFromFile("C:\Users\Administrator\Desktop\sample.pdf")
    
                'Load an image
                Dim image As Image =  Image.FromFile("C:\Users\Administrator\Desktop\logo.png")
    
                'Get the image width and height
                Dim imgWidth As Integer =  image.Width
                Dim imgHeight As Integer =  image.Height
    
                'Loop through the pages
                Dim i As Integer
                For  i = 0 To  document.Pages.Count- 1  Step  i + 1
                    'Get the page width and height
                    Dim pageWidth As single =  document.Pages(i).ActualSize.Width
                    Dim pageHeight As single =  document.Pages(i).ActualSize.Height
    
                    'Set the background opacity
                    document.Pages(i).BackgroudOpacity = 0.3f
    
                    'Set the background image of current page
                    document.Pages(i).BackgroundImage = image
    
                    'Position the background image at the center of the page
                    Dim rect As Rectangle =  New Rectangle(CType((pageWidth - imgWidth) / 2,(Integer)(pageHeight - imgHeight) / 2,imgWidth,imgHeight, Integer))
                    document.Pages(i).BackgroundRegion = rect
                Next
    
                'Save the document to file
                document.SaveToFile("AddImageWatermark.pdf")
                document.Close()
            End Sub
        End Class
    End Namespace

PM> Install-Package Spire.PDF 

using Spire.Pdf;
    using System.Drawing;
    
    namespace AddImageWatermark
    {
        class Program
        {
            static void Main(string[] args)
            {
                //Create a PdfDocument object
                PdfDocument document = new PdfDocument();
    
                //Load a sample PDF document
                document.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.pdf");
    
                //Load an image
                Image image = Image.FromFile(@"C:\Users\Administrator\Desktop\logo.png");
    
                //Get the image width and height
                int imgWidth = image.Width;
                int imgHeight = image.Height;
    
                //Loop through the pages
                for (int i = 0; i < document.Pages.Count; i++)
                {
                    //Get the page width and height
                    float pageWidth = document.Pages[i].ActualSize.Width;
                    float pageHeight = document.Pages[i].ActualSize.Height;
    
                    //Set the background opacity
                    document.Pages[i].BackgroudOpacity = 0.3f;
    
                    //Set the background image of current page
                    document.Pages[i].BackgroundImage = image;
    
                    //Position the background image at the center of the page
                    Rectangle rect = new Rectangle((int)(pageWidth - imgWidth) / 2, (int)(pageHeight - imgHeight) / 2, imgWidth, imgHeight);
                    document.Pages[i].BackgroundRegion = rect;
                }
    
                //Save the document to file
                document.SaveToFile("AddImageWatermark.pdf");
                document.Close();
            }
        }
    }

Imports Spire.Pdf
    Imports System.Drawing
    
    Namespace AddImageWatermark
        Class Program
            Shared  Sub Main(ByVal args() As String)
                'Create a PdfDocument object
                Dim document As PdfDocument =  New PdfDocument()
    
                'Load a sample PDF document
                document.LoadFromFile("C:\Users\Administrator\Desktop\sample.pdf")
    
                'Load an image
                Dim image As Image =  Image.FromFile("C:\Users\Administrator\Desktop\logo.png")
    
                'Get the image width and height
                Dim imgWidth As Integer =  image.Width
                Dim imgHeight As Integer =  image.Height
    
                'Loop through the pages
                Dim i As Integer
                For  i = 0 To  document.Pages.Count- 1  Step  i + 1
                    'Get the page width and height
                    Dim pageWidth As single =  document.Pages(i).ActualSize.Width
                    Dim pageHeight As single =  document.Pages(i).ActualSize.Height
    
                    'Set the background opacity
                    document.Pages(i).BackgroudOpacity = 0.3f
    
                    'Set the background image of current page
                    document.Pages(i).BackgroundImage = image
    
                    'Position the background image at the center of the page
                    Dim rect As Rectangle =  New Rectangle(CType((pageWidth - imgWidth) / 2,(Integer)(pageHeight - imgHeight) / 2,imgWidth,imgHeight, Integer))
                    document.Pages(i).BackgroundRegion = rect
                Next
    
                'Save the document to file
                document.SaveToFile("AddImageWatermark.pdf")
                document.Close()
            End Sub
        End Class
    End Namespace

PM> Install-Package Spire.PDF 

using Spire.Pdf;
    using System.Drawing;
    
    namespace AddImageWatermark
    {
        class Program
        {
            static void Main(string[] args)
            {
                //Create a PdfDocument object
                PdfDocument document = new PdfDocument();
    
                //Load a sample PDF document
                document.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.pdf");
    
                //Load an image
                Image image = Image.FromFile(@"C:\Users\Administrator\Desktop\logo.png");
    
                //Get the image width and height
                int imgWidth = image.Width;
                int imgHeight = image.Height;
    
                //Loop through the pages
                for (int i = 0; i < document.Pages.Count; i++)
                {
                    //Get the page width and height
                    float pageWidth = document.Pages[i].ActualSize.Width;
                    float pageHeight = document.Pages[i].ActualSize.Height;
    
                    //Set the background opacity
                    document.Pages[i].BackgroudOpacity = 0.3f;
    
                    //Set the background image of current page
                    document.Pages[i].BackgroundImage = image;
    
                    //Position the background image at the center of the page
                    Rectangle rect = new Rectangle((int)(pageWidth - imgWidth) / 2, (int)(pageHeight - imgHeight) / 2, imgWidth, imgHeight);
                    document.Pages[i].BackgroundRegion = rect;
                }
    
                //Save the document to file
                document.SaveToFile("AddImageWatermark.pdf");
                document.Close();
            }
        }
    }

Imports Spire.Pdf
    Imports System.Drawing
    
    Namespace AddImageWatermark
        Class Program
            Shared  Sub Main(ByVal args() As String)
                'Create a PdfDocument object
                Dim document As PdfDocument =  New PdfDocument()
    
                'Load a sample PDF document
                document.LoadFromFile("C:\Users\Administrator\Desktop\sample.pdf")
    
                'Load an image
                Dim image As Image =  Image.FromFile("C:\Users\Administrator\Desktop\logo.png")
    
                'Get the image width and height
                Dim imgWidth As Integer =  image.Width
                Dim imgHeight As Integer =  image.Height
    
                'Loop through the pages
                Dim i As Integer
                For  i = 0 To  document.Pages.Count- 1  Step  i + 1
                    'Get the page width and height
                    Dim pageWidth As single =  document.Pages(i).ActualSize.Width
                    Dim pageHeight As single =  document.Pages(i).ActualSize.Height
    
                    'Set the background opacity
                    document.Pages(i).BackgroudOpacity = 0.3f
    
                    'Set the background image of current page
                    document.Pages(i).BackgroundImage = image
    
                    'Position the background image at the center of the page
                    Dim rect As Rectangle =  New Rectangle(CType((pageWidth - imgWidth) / 2,(Integer)(pageHeight - imgHeight) / 2,imgWidth,imgHeight, Integer))
                    document.Pages(i).BackgroundRegion = rect
                Next
    
                'Save the document to file
                document.SaveToFile("AddImageWatermark.pdf")
                document.Close()
            End Sub
        End Class
    End Namespace

PM> Install-Package Spire.PDF 

using Spire.Pdf;
    using System.Drawing;
    
    namespace AddImageWatermark
    {
        class Program
        {
            static void Main(string[] args)
            {
                //Create a PdfDocument object
                PdfDocument document = new PdfDocument();
    
                //Load a sample PDF document
                document.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.pdf");
    
                //Load an image
                Image image = Image.FromFile(@"C:\Users\Administrator\Desktop\logo.png");
    
                //Get the image width and height
                int imgWidth = image.Width;
                int imgHeight = image.Height;
    
                //Loop through the pages
                for (int i = 0; i < document.Pages.Count; i++)
                {
                    //Get the page width and height
                    float pageWidth = document.Pages[i].ActualSize.Width;
                    float pageHeight = document.Pages[i].ActualSize.Height;
    
                    //Set the background opacity
                    document.Pages[i].BackgroudOpacity = 0.3f;
    
                    //Set the background image of current page
                    document.Pages[i].BackgroundImage = image;
    
                    //Position the background image at the center of the page
                    Rectangle rect = new Rectangle((int)(pageWidth - imgWidth) / 2, (int)(pageHeight - imgHeight) / 2, imgWidth, imgHeight);
                    document.Pages[i].BackgroundRegion = rect;
                }
    
                //Save the document to file
                document.SaveToFile("AddImageWatermark.pdf");
                document.Close();
            }
        }
    }

Imports Spire.Pdf
    Imports System.Drawing
    
    Namespace AddImageWatermark
        Class Program
            Shared  Sub Main(ByVal args() As String)
                'Create a PdfDocument object
                Dim document As PdfDocument =  New PdfDocument()
    
                'Load a sample PDF document
                document.LoadFromFile("C:\Users\Administrator\Desktop\sample.pdf")
    
                'Load an image
                Dim image As Image =  Image.FromFile("C:\Users\Administrator\Desktop\logo.png")
    
                'Get the image width and height
                Dim imgWidth As Integer =  image.Width
                Dim imgHeight As Integer =  image.Height
    
                'Loop through the pages
                Dim i As Integer
                For  i = 0 To  document.Pages.Count- 1  Step  i + 1
                    'Get the page width and height
                    Dim pageWidth As single =  document.Pages(i).ActualSize.Width
                    Dim pageHeight As single =  document.Pages(i).ActualSize.Height
    
                    'Set the background opacity
                    document.Pages(i).BackgroudOpacity = 0.3f
    
                    'Set the background image of current page
                    document.Pages(i).BackgroundImage = image
    
                    'Position the background image at the center of the page
                    Dim rect As Rectangle =  New Rectangle(CType((pageWidth - imgWidth) / 2,(Integer)(pageHeight - imgHeight) / 2,imgWidth,imgHeight, Integer))
                    document.Pages(i).BackgroundRegion = rect
                Next
    
                'Save the document to file
                document.SaveToFile("AddImageWatermark.pdf")
                document.Close()
            End Sub
        End Class
    End Namespace

PM> Install-Package Spire.PDF 

using Spire.Pdf;
    using System.Drawing;
    
    namespace AddImageWatermark
    {
        class Program
        {
            static void Main(string[] args)
            {
                //Create a PdfDocument object
                PdfDocument document = new PdfDocument();
    
                //Load a sample PDF document
                document.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.pdf");
    
                //Load an image
                Image image = Image.FromFile(@"C:\Users\Administrator\Desktop\logo.png");
    
                //Get the image width and height
                int imgWidth = image.Width;
                int imgHeight = image.Height;
    
                //Loop through the pages
                for (int i = 0; i < document.Pages.Count; i++)
                {
                    //Get the page width and height
                    float pageWidth = document.Pages[i].ActualSize.Width;
                    float pageHeight = document.Pages[i].ActualSize.Height;
    
                    //Set the background opacity
                    document.Pages[i].BackgroudOpacity = 0.3f;
    
                    //Set the background image of current page
                    document.Pages[i].BackgroundImage = image;
    
                    //Position the background image at the center of the page
                    Rectangle rect = new Rectangle((int)(pageWidth - imgWidth) / 2, (int)(pageHeight - imgHeight) / 2, imgWidth, imgHeight);
                    document.Pages[i].BackgroundRegion = rect;
                }
    
                //Save the document to file
                document.SaveToFile("AddImageWatermark.pdf");
                document.Close();
            }
        }
    }

Imports Spire.Pdf
    Imports System.Drawing
    
    Namespace AddImageWatermark
        Class Program
            Shared  Sub Main(ByVal args() As String)
                'Create a PdfDocument object
                Dim document As PdfDocument =  New PdfDocument()
    
                'Load a sample PDF document
                document.LoadFromFile("C:\Users\Administrator\Desktop\sample.pdf")
    
                'Load an image
                Dim image As Image =  Image.FromFile("C:\Users\Administrator\Desktop\logo.png")
    
                'Get the image width and height
                Dim imgWidth As Integer =  image.Width
                Dim imgHeight As Integer =  image.Height
    
                'Loop through the pages
                Dim i As Integer
                For  i = 0 To  document.Pages.Count- 1  Step  i + 1
                    'Get the page width and height
                    Dim pageWidth As single =  document.Pages(i).ActualSize.Width
                    Dim pageHeight As single =  document.Pages(i).ActualSize.Height
    
                    'Set the background opacity
                    document.Pages(i).BackgroudOpacity = 0.3f
    
                    'Set the background image of current page
                    document.Pages(i).BackgroundImage = image
    
                    'Position the background image at the center of the page
                    Dim rect As Rectangle =  New Rectangle(CType((pageWidth - imgWidth) / 2,(Integer)(pageHeight - imgHeight) / 2,imgWidth,imgHeight, Integer))
                    document.Pages(i).BackgroundRegion = rect
                Next
    
                'Save the document to file
                document.SaveToFile("AddImageWatermark.pdf")
                document.Close()
            End Sub
        End Class
    End Namespace

PM> Install-Package Spire.PDF 

using Spire.Pdf;
    using System.Drawing;
    
    namespace AddImageWatermark
    {
        class Program
        {
            static void Main(string[] args)
            {
                //Create a PdfDocument object
                PdfDocument document = new PdfDocument();
    
                //Load a sample PDF document
                document.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.pdf");
    
                //Load an image
                Image image = Image.FromFile(@"C:\Users\Administrator\Desktop\logo.png");
    
                //Get the image width and height
                int imgWidth = image.Width;
                int imgHeight = image.Height;
    
                //Loop through the pages
                for (int i = 0; i < document.Pages.Count; i++)
                {
                    //Get the page width and height
                    float pageWidth = document.Pages[i].ActualSize.Width;
                    float pageHeight = document.Pages[i].ActualSize.Height;
    
                    //Set the background opacity
                    document.Pages[i].BackgroudOpacity = 0.3f;
    
                    //Set the background image of current page
                    document.Pages[i].BackgroundImage = image;
    
                    //Position the background image at the center of the page
                    Rectangle rect = new Rectangle((int)(pageWidth - imgWidth) / 2, (int)(pageHeight - imgHeight) / 2, imgWidth, imgHeight);
                    document.Pages[i].BackgroundRegion = rect;
                }
    
                //Save the document to file
                document.SaveToFile("AddImageWatermark.pdf");
                document.Close();
            }
        }
    }

Imports Spire.Pdf
    Imports System.Drawing
    
    Namespace AddImageWatermark
        Class Program
            Shared  Sub Main(ByVal args() As String)
                'Create a PdfDocument object
                Dim document As PdfDocument =  New PdfDocument()
    
                'Load a sample PDF document
                document.LoadFromFile("C:\Users\Administrator\Desktop\sample.pdf")
    
                'Load an image
                Dim image As Image =  Image.FromFile("C:\Users\Administrator\Desktop\logo.png")
    
                'Get the image width and height
                Dim imgWidth As Integer =  image.Width
                Dim imgHeight As Integer =  image.Height
    
                'Loop through the pages
                Dim i As Integer
                For  i = 0 To  document.Pages.Count- 1  Step  i + 1
                    'Get the page width and height
                    Dim pageWidth As single =  document.Pages(i).ActualSize.Width
                    Dim pageHeight As single =  document.Pages(i).ActualSize.Height
    
                    'Set the background opacity
                    document.Pages(i).BackgroudOpacity = 0.3f
    
                    'Set the background image of current page
                    document.Pages(i).BackgroundImage = image
    
                    'Position the background image at the center of the page
                    Dim rect As Rectangle =  New Rectangle(CType((pageWidth - imgWidth) / 2,(Integer)(pageHeight - imgHeight) / 2,imgWidth,imgHeight, Integer))
                    document.Pages(i).BackgroundRegion = rect
                Next
    
                'Save the document to file
                document.SaveToFile("AddImageWatermark.pdf")
                document.Close()
            End Sub
        End Class
    End Namespace

PM> Install-Package Spire.PDF 

using Spire.Pdf;
    using Spire.Pdf.Graphics;
    using System.Drawing;
    
    namespace AddTextWatermarkToPdf
    {
        class Program
        {
            static void Main(string[] args)
            {
                //Create a PdfDocument object
                PdfDocument pdf = new PdfDocument();
    
                //Load a sample PDF document
                pdf.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.pdf");
    
                //Create a PdfTrueTypeFont object
                PdfTrueTypeFont font = new PdfTrueTypeFont(new Font("Arial", 50f), true);
    
                //Set the watermark text
                string text = "CONFIDENTIAL";
    
                //Measure the text size
                SizeF textSize = font.MeasureString(text);
    
                //Calculate the values of two offset variables,
                //which will be used to calculate the translation amount of the coordinate system
                float offset1 = (float)(textSize.Width * System.Math.Sqrt(2) / 4);
                float offset2 = (float)(textSize.Height * System.Math.Sqrt(2) / 4);
    
                //Traverse all the pages in the document
                foreach (PdfPageBase page in pdf.Pages)
                {
                    //Set the page transparency
                    page.Canvas.SetTransparency(0.8f);
    
                    //Translate the coordinate system by specified coordinates
                    page.Canvas.TranslateTransform(page.Canvas.Size.Width / 2 - offset1 - offset2, page.Canvas.Size.Height / 2 + offset1 - offset2);
    
                    //Rotate the coordinate system 45 degrees counterclockwise
                    page.Canvas.RotateTransform(-45);
    
                    //Draw watermark text on the page
                    page.Canvas.DrawString(text, font, PdfBrushes.DarkGray, 0, 0);
                }
    
                //Save the changes to another file
                pdf.SaveToFile("TextWatermark.pdf");
            }
        }
    }

Imports Spire.Pdf
    Imports Spire.Pdf.Graphics
    Imports System.Drawing
    
    Namespace AddTextWatermarkToPdf
        Class Program
            Shared  Sub Main(ByVal args() As String)
                'Create a PdfDocument object
                Dim pdf As PdfDocument =  New PdfDocument()
    
                'Load a sample PDF document
                pdf.LoadFromFile("C:\Users\Administrator\Desktop\sample.pdf")
    
                'Create a PdfTrueTypeFont object
                Dim font As PdfTrueTypeFont =  New PdfTrueTypeFont(New Font("Arial",50f),True)
    
                'Set the watermark text
                Dim text As String =  "CONFIDENTIAL"
    
                'Measure the text size
                Dim textSize As SizeF =  font.MeasureString(text)
    
                'Calculate the values of two offset variables,
                'which will be used to calculate the translation amount of the coordinate system
                Dim offset1 As single = CType((textSize.Width * System.Math.Sqrt(2) / 4), single)
                Dim offset2 As single = CType((textSize.Height * System.Math.Sqrt(2) / 4), single)
    
                'Traverse all the pages in the document
                Dim page As PdfPageBase
                For Each page In pdf.Pages
                    'Set the page transparency
                    page.Canvas.SetTransparency(0.8f)
    
                    'Translate the coordinate system by specified coordinates
                    page.Canvas.TranslateTransform(page.Canvas.Size.Width / 2 - offset1 - offset2, page.Canvas.Size.Height / 2 + offset1 - offset2)
    
                    'Rotate the coordinate system 45 degrees counterclockwise
                    page.Canvas.RotateTransform(-45)
    
                    'Draw watermark text on the page
                    page.Canvas.DrawString(text, font, PdfBrushes.DarkGray, 0, 0)
                Next
    
                'Save the changes to another file
                pdf.SaveToFile("TextWatermark.pdf")
            End Sub
        End Class
    End Namespace

using System;
    using Spire.Pdf;
    using Spire.Pdf.Graphics;
    using System.Drawing;
    
    namespace AddMultiLineTextWatermark
    {
        class Program
        {
            static void Main(string[] args)
            {
                //Create a PdfDocument instance
                PdfDocument pdf = new PdfDocument();
    
                //Load a sample PDF document
                pdf.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.pdf");
    
                //Create a PdfTrueTypeFont object
                PdfTrueTypeFont font = new PdfTrueTypeFont(new Font("Arial", 20f), true);
    
                //Traverse all the pages
                for (int i = 0; i < pdf.Pages.Count; i++)
                {
                    //Call InsertMultiLineTextWatermark() method to add text watermarks to the specified page
                    InsertMultiLineTextWatermark(pdf.Pages[i], "E-ICEBLUE CO LTD", font, 3, 3);
                }
    
                //Save the document to another file
                pdf.SaveToFile("MultiLineTextWatermark.pdf");
            }
    
            //Create a custom method to insert multi-line text watermarks to a page
            static void InsertMultiLineTextWatermark(PdfPageBase page, String watermarkText, PdfTrueTypeFont font, int rowNum, int columnNum)
            {
                //Measure the text size
                SizeF textSize = font.MeasureString(watermarkText);
    
                //Calculate the values of two offset variables, which will be used to calculate the translation amount of coordinate system
                float offset1 = (float)(textSize.Width * System.Math.Sqrt(2) / 4);
                float offset2 = (float)(textSize.Height * System.Math.Sqrt(2) / 4);
    
                //Create a tile brush
                PdfTilingBrush brush = new PdfTilingBrush(new SizeF(page.ActualSize.Width / columnNum, page.ActualSize.Height / rowNum));
                brush.Graphics.SetTransparency(0.3f);
                brush.Graphics.Save();
                brush.Graphics.TranslateTransform(brush.Size.Width / 2 - offset1 - offset2, brush.Size.Height / 2 + offset1 - offset2);
                brush.Graphics.RotateTransform(-45);
    
                //Draw watermark text on the tile brush
                brush.Graphics.DrawString(watermarkText, font, PdfBrushes.Violet, 0, 0);
                brush.Graphics.Restore();
    
                //Draw a rectangle (that covers the whole page) using the tile brush
                page.Canvas.DrawRectangle(brush, new RectangleF(new PointF(0, 0), page.ActualSize));
            }
        }
    }

Imports System
    Imports Spire.Pdf
    Imports Spire.Pdf.Graphics
    Imports System.Drawing
    
    Namespace AddMultiLineTextWatermark
        Class Program
            Shared  Sub Main(ByVal args() As String)
                'Create a PdfDocument instance
                Dim pdf As PdfDocument =  New PdfDocument()
    
                'Load a sample PDF document
                pdf.LoadFromFile("C:\Users\Administrator\Desktop\sample.pdf")
    
                'Create a PdfTrueTypeFont object
                Dim font As PdfTrueTypeFont =  New PdfTrueTypeFont(New Font("Arial",20f),True)
    
                'Traverse all the pages
                Dim i As Integer
                For  i = 0 To  pdf.Pages.Count- 1  Step  i + 1
                    'Call InsertMultiLineTextWatermark() method to add text watermarks to the specified page
                    InsertMultiLineTextWatermark(pdf.Pages(i), "E-ICEBLUE CO LTD", font, 3, 3)
                Next
    
                'Save the document to another file
                pdf.SaveToFile("MultiLineTextWatermark.pdf")
            End Sub
    
            'Create a custom method to insert multi-line text watermarks to a page
            Shared  Sub InsertMultiLineTextWatermark(ByVal page As PdfPageBase, ByVal watermarkText As String, ByVal font As PdfTrueTypeFont, ByVal rowNum As Integer, ByVal columnNum As Integer)
                'Measure the text size
                Dim textSize As SizeF =  font.MeasureString(watermarkText)
    
                'Calculate the values of two offset variables, which will be used to calculate the translation amount of coordinate system
                Dim offset1 As single = CType((textSize.Width * System.Math.Sqrt(2) / 4), single)
                Dim offset2 As single = CType((textSize.Height * System.Math.Sqrt(2) / 4), single)
    
                'Create a tile brush
                Dim brush As PdfTilingBrush =  New PdfTilingBrush(New SizeF(page.ActualSize.Width / columnNum,page.ActualSize.Height / rowNum))
                brush.Graphics.SetTransparency(0.3f)
                brush.Graphics.Save()
                brush.Graphics.TranslateTransform(brush.Size.Width / 2 - offset1 - offset2, brush.Size.Height / 2 + offset1 - offset2)
                brush.Graphics.RotateTransform(-45)
    
                'Draw watermark text on the tile brush
                brush.Graphics.DrawString(watermarkText, font, PdfBrushes.Violet, 0, 0)
                brush.Graphics.Restore()
    
                'Draw a rectangle (that covers the whole page) using the tile brush
                page.Canvas.DrawRectangle(brush, New RectangleF(New PointF(0, 0), page.ActualSize))
            End Sub
        End Class
    End Namespace