PM> Install-Package Spire.PDF

using Spire.Pdf;
using Spire.Pdf.Security;
using System;
using System.Drawing;
using Spire.Pdf.Graphics;

namespace AddTextSignature
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a PdfDocument object
            PdfDocument doc = new PdfDocument();

            //Load a sample PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\sample.pdf");

            //Load the certificate 
            PdfCertificate cert = new PdfCertificate("C:\\Users\\Administrator\\Desktop\\MyCertificate.pfx", "e-iceblue");

            //Create a PdfSignature object and specify its position and size 
            PdfSignature signature = new PdfSignature(doc, doc.Pages[doc.Pages.Count-1], cert, "MySignature");     
            RectangleF rectangleF = new RectangleF(doc.Pages[0].ActualSize.Width - 340, 150, 290, 100);
            signature.Bounds = rectangleF;
            signature.Certificated = true;

            //Set the graphics mode to sign detail
            signature.GraphicsMode = GraphicMode.SignDetail;

            //Set the signature content 
            signature.NameLabel = "Signer:";
            signature.Name = "Gary";
            signature.ContactInfoLabel = "Phone:";
            signature.ContactInfo = "0123456";
            signature.DateLabel = "Date:";
            signature.Date = DateTime.Now;
            signature.LocationInfoLabel = "Location:";
            signature.LocationInfo = "USA";
            signature.ReasonLabel = "Reason:";
            signature.Reason = "I am the author";
            signature.DistinguishedNameLabel = "DN:";
            signature.DistinguishedName = signature.Certificate.IssuerName.Name;

            //Set the signature font 
            signature.SignDetailsFont = new PdfTrueTypeFont(new Font("Arial Unicode MS",12f,FontStyle.Regular));

            //Set the document permission to forbid changes but allow form fill
            signature.DocumentPermissions = PdfCertificationFlags.ForbidChanges | PdfCertificationFlags.AllowFormFill;

            //Save to file 
            doc.SaveToFile("TextSignature.pdf");
            doc.Close();
        }
    }
}

Imports Spire.Pdf
Imports Spire.Pdf.Security
Imports System
Imports System.Drawing
Imports Spire.Pdf.Graphics
 
Namespace AddTextSignature
    Class Program
        Shared  Sub Main(ByVal args() As String)
            'Create a PdfDocument object
            Dim doc As PdfDocument =  New PdfDocument() 
 
            'Load a sample PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\sample.pdf")
 
            'Load the certificate 
            Dim cert As PdfCertificate =  New PdfCertificate("C:\\Users\\Administrator\\Desktop\\MyCertificate.pfx","e-iceblue") 
 
            'Create a PdfSignature object and specify its position and size 
            Dim signature As PdfSignature =  New PdfSignature(doc,doc.Pages(doc.Pages.Count-1),cert,"MySignature") 
            Dim rectangleF As RectangleF =  New RectangleF(doc.Pages(0).ActualSize.Width - 340,150,290,100) 
            signature.Bounds = rectangleF
            signature.Certificated = True
 
            'Set the graphics mode to sign detail
            signature.GraphicsMode = GraphicMode.SignDetail
 
            'Set the signature content 
            signature.NameLabel = "Signer:"
            signature.Name = "Gary"
            signature.ContactInfoLabel = "Phone:"
            signature.ContactInfo = "0123456"
            signature.DateLabel = "Date:"
            signature.Date = DateTime.Now
            signature.LocationInfoLabel = "Location:"
            signature.LocationInfo = "USA"
            signature.ReasonLabel = "Reason:"
            signature.Reason = "I am the author"
            signature.DistinguishedNameLabel = "DN:"
            signature.DistinguishedName = signature.Certificate.IssuerName.Name

            'Set the signature font 
            signature.SignDetailsFont = New PdfTrueTypeFont(New Font("Arial Unicode MS",12f,FontStyle.Regular))
 
            'Set the document permission to forbid changes but allow form fill
            signature.DocumentPermissions = PdfCertificationFlags.ForbidChanges | PdfCertificationFlags.AllowFormFill
 
            'Save to file 
            doc.SaveToFile("TextSignature.pdf")
            doc.Close()
        End Sub
    End Class
End Namespace

using Spire.Pdf;
using Spire.Pdf.Graphics;
using Spire.Pdf.Security;
using System.Drawing;

namespace AddImageSignature
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a PdfDocument object
            PdfDocument doc = new PdfDocument();

            //Load a sample PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\sample.pdf");

            //Load the certificate 
            PdfCertificate cert = new PdfCertificate("C:\\Users\\Administrator\\Desktop\\MyCertificate.pfx", "e-iceblue");

            //Create a PdfSignature object and specify its position and size 
            PdfSignature signature = new PdfSignature(doc, doc.Pages[doc.Pages.Count - 1], cert, "MySignature");
            RectangleF rectangleF = new RectangleF(doc.Pages[0].ActualSize.Width - 200, 150, 130, 130);
            signature.Bounds = rectangleF;
            signature.Certificated = true;

            //Set the graphics mode to image only
            signature.GraphicsMode = GraphicMode.SignImageOnly;

            //Set the sign image source
            signature.SignImageSource = PdfImage.FromFile("C:\\Users\\Administrator\\Desktop\\verified.png");
            signature.SignImageLayout = SignImageLayout.Stretch; 

            //Set the signature font 
            signature.SignDetailsFont = new PdfTrueTypeFont(new Font("Arial Unicode MS", 12f, FontStyle.Regular));

            //Set the document permission to forbid changes but allow form fill
            signature.DocumentPermissions = PdfCertificationFlags.ForbidChanges | PdfCertificationFlags.AllowFormFill;

            //Save to file 
            doc.SaveToFile("ImageSignature.pdf");
            doc.Close();
        }
    }
}

Imports Spire.Pdf
Imports Spire.Pdf.Graphics
Imports Spire.Pdf.Security
Imports System.Drawing
 
Namespace AddImageSignature
    Class Program
        Shared  Sub Main(ByVal args() As String)
            'Create a PdfDocument object
            Dim doc As PdfDocument =  New PdfDocument() 
 
            'Load a sample PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\sample.pdf")
 
            'Load the certificate 
            Dim cert As PdfCertificate =  New PdfCertificate("C:\\Users\\Administrator\\Desktop\\MyCertificate.pfx","e-iceblue") 
 
            'Create a PdfSignature object and specify its position and size 
            Dim signature As PdfSignature =  New PdfSignature(doc,doc.Pages(doc.Pages.Count - 1),cert,"MySignature") 
            Dim rectangleF As RectangleF =  New RectangleF(doc.Pages(0).ActualSize.Width - 200,150,130,130) 
            signature.Bounds = rectangleF
            signature.Certificated = True
 
            'Set the graphics mode to image only
            signature.GraphicsMode = GraphicMode.SignImageOnly
 
            'Set the sign image source
            signature.SignImageSource = PdfImage.FromFile("C:\\Users\\Administrator\\Desktop\\verified.png")
 
            'Set the signature font 
            signature.SignDetailsFont = New PdfTrueTypeFont(New Font("Arial Unicode MS", 12f, FontStyle.Regular))
 
            'Set the document permission to forbid changes but allow form fill
            signature.DocumentPermissions = PdfCertificationFlags.ForbidChanges | PdfCertificationFlags.AllowFormFill
 
            'Save to file 
            doc.SaveToFile("ImageSignature.pdf")
            doc.Close()
        End Sub
    End Class
End Namespace

using Spire.Pdf;
using Spire.Pdf.Security;
using System;
using System.Drawing;
using Spire.Pdf.Graphics;

namespace AddTextAndImageSignature
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a PdfDocument object
            PdfDocument doc = new PdfDocument();

            //Load a sample PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\sample.pdf");

            //Load the certificate 
            PdfCertificate cert = new PdfCertificate("C:\\Users\\Administrator\\Desktop\\MyCertificate.pfx", "e-iceblue");

            //Create a PdfSignature object and specify its position and size 
            PdfSignature signature = new PdfSignature(doc, doc.Pages[doc.Pages.Count - 1], cert, "MySignature");
            RectangleF rectangleF = new RectangleF(doc.Pages[0].ActualSize.Width - 320, 150, 260, 110);
            signature.Bounds = rectangleF;
            signature.Certificated = true;

            //Set the graphics mode to image and sign detail
            signature.GraphicsMode = GraphicMode.SignImageAndSignDetail;

            //Set the signature content 
            signature.NameLabel = "Signer:";
            signature.Name = "Gary";
            signature.ContactInfoLabel = "Phone:";
            signature.ContactInfo = "0123456";
            signature.DateLabel = "Date:";
            signature.Date = DateTime.Now;
            signature.LocationInfoLabel = "Location:";
            signature.LocationInfo = "USA";
            signature.ReasonLabel = "Reason:";
            signature.Reason = "I am the author";
            signature.DistinguishedNameLabel = "DN:";
            signature.DistinguishedName = signature.Certificate.IssuerName.Name;

            //Set the signature image source
            signature.SignImageSource = PdfImage.FromFile("C:\\Users\\Administrator\\Desktop\\handSignature.png");

            //Set the signature font 
            signature.SignDetailsFont = new PdfTrueTypeFont(new Font("Arial Unicode MS", 12f, FontStyle.Regular));

            //Set the document permission to forbid changes but allow form fill
            signature.DocumentPermissions = PdfCertificationFlags.ForbidChanges | PdfCertificationFlags.AllowFormFill;

            //Save to file 
            doc.SaveToFile("TextAndImageSignature.pdf");
            doc.Close();
        }
    }
}

Imports Spire.Pdf
Imports Spire.Pdf.Security
Imports System
Imports System.Drawing
Imports Spire.Pdf.Graphics
 
Namespace AddTextAndImageSignature
    Class Program
        Shared  Sub Main(ByVal args() As String)
            'Create a PdfDocument object
            Dim doc As PdfDocument =  New PdfDocument() 
 
            'Load a sample PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\sample.pdf")
 
            'Load the certificate 
            Dim cert As PdfCertificate =  New PdfCertificate("C:\\Users\\Administrator\\Desktop\\MyCertificate.pfx","e-iceblue") 
 
            'Create a PdfSignature object and specify its position and size 
            Dim signature As PdfSignature =  New PdfSignature(doc,doc.Pages(doc.Pages.Count - 1),cert,"MySignature") 
            Dim rectangleF As RectangleF =  New RectangleF(doc.Pages(0).ActualSize.Width - 320,150,260,110) 
            signature.Bounds = rectangleF
            signature.Certificated = True
 
            'Set the graphics mode to image and sign detail
            signature.GraphicsMode = GraphicMode.SignImageAndSignDetail
 
            'Set the signature content 
            signature.NameLabel = "Signer:"
            signature.Name = "Gary"
            signature.ContactInfoLabel = "Phone:"
            signature.ContactInfo = "0123456"
            signature.DateLabel = "Date:"
            signature.Date = DateTime.Now
            signature.LocationInfoLabel = "Location:"
            signature.LocationInfo = "USA"
            signature.ReasonLabel = "Reason:"
            signature.Reason = "I am the author"
            signature.DistinguishedNameLabel = "DN:"
            signature.DistinguishedName = signature.Certificate.IssuerName.Name
 
            'Set the signature image source
            signature.SignImageSource = PdfImage.FromFile("C:\\Users\\Administrator\\Desktop\\handSignature.png")
 
            'Set the signature font 
            signature.SignDetailsFont = New PdfTrueTypeFont(New Font("Arial Unicode MS", 12f, FontStyle.Regular))
 
            'Set the document permission to forbid changes but allow form fill
            signature.DocumentPermissions = PdfCertificationFlags.ForbidChanges | PdfCertificationFlags.AllowFormFill
 
            'Save to file 
            doc.SaveToFile("TextAndImageSignature.pdf")
            doc.Close()
        End Sub
    End Class
End Namespace

PM> Install-Package Spire.PDF 

using Spire.Pdf;
using Spire.Pdf.Security;
using Spire.Pdf.Widget;

namespace GetSignatureCertificate
{
    class Program
    {
        static void Main(string[] args)
        {

            //Create a PdfDocument object
            PdfDocument pdf = new PdfDocument();

            //Load a PDF file
            pdf.LoadFromFile("PDFSignature.pdf");

            //Get a collection of form fields in the PDF file
            PdfFormWidget pdfFormWidget = (PdfFormWidget)pdf.Form;
            PdfFormFieldWidgetCollection pdfFormFieldWidgetCollection = pdfFormWidget.FieldsWidget;

            //Iterate through all fields
            for (int i = 0; i < pdfFormFieldWidgetCollection.Count; i++)
            {
                //Get the signature fields
                if (pdfFormFieldWidgetCollection[i] is PdfSignatureFieldWidget)
                {
                    PdfSignatureFieldWidget signatureFieldWidget = (PdfSignatureFieldWidget)pdfFormFieldWidgetCollection[i];

                    //Get the signatures
                    PdfSignature signature = signatureFieldWidget.Signature;

                    //Verify signatures
                    bool valid = signature.VerifySignature();
                    if (valid)
                    {
                        Console.WriteLine("Valid signatures");
                    }
                    else
                    {
                        Console.WriteLine("Invalid signatures");
                    }
                }
            }
        }
    }
}

using Spire.Pdf;
using Spire.Pdf.Security;
using Spire.Pdf.Widget;

namespace GetSignatureCertificate
{
    class Program
    {
        static void Main(string[] args)
        {

            //Create a PdfDocument object
            PdfDocument pdf = new PdfDocument();

            //Load a PDF document
            pdf.LoadFromFile("PDFSignature.pdf");

            //Get a collection of form fields in the PDF file
            PdfFormWidget pdfFormWidget = (PdfFormWidget)pdf.Form;
            PdfFormFieldWidgetCollection pdfFormFieldWidgetCollection = pdfFormWidget.FieldsWidget;

            for (int i = 0; i < pdfFormFieldWidgetCollection.Count; i++)
            {
                //Get the signature fields
                if (pdfFormFieldWidgetCollection[i] is PdfSignatureFieldWidget)
                {
                    PdfSignatureFieldWidget signatureFieldWidget = (PdfSignatureFieldWidget)pdfFormFieldWidgetCollection[i];

                    //Get the signatures
                    PdfSignature signature = signatureFieldWidget.Signature;

                    //Check if the document has been modified after signing
                    bool modified = signature.VerifyDocModified();
                    if (modified)
                    {
                        Console.WriteLine("The document has been modified.");
                    }
                    else
                    {
                        Console.WriteLine("The document has not been modified.");
                    }
                }
            }
        }
    }
}

using Spire.Pdf;
using Spire.Pdf.Widget;

namespace GetSignatureCertificate
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a PdfDocument object
            PdfDocument pdf = new PdfDocument();

            //Load a PDF file
            pdf.LoadFromFile("PDFSignature.pdf");

            //Get a collection of form fields in the PDF file
            PdfFormWidget pdfFormWidget = (PdfFormWidget)pdf.Form;
            PdfFormFieldWidgetCollection pdfFormFieldWidgetCollection = pdfFormWidget.FieldsWidget;

            //Iterate through all fields
            for (int i = 0; i < pdfFormFieldWidgetCollection.Count; i++)
            {
                //Get the signature fields
                if (pdfFormFieldWidgetCollection[i] is PdfSignatureFieldWidget)
                {
                    PdfSignatureFieldWidget signatureFieldWidget = (PdfSignatureFieldWidget)pdfFormFieldWidgetCollection[i];

                    //Get the certificate of the signature
                    string certificateInfo = signatureFieldWidget.Signature.Certificate.ToString();

                    //Get the format of the certificate
                    string format = signatureFieldWidget.Signature.Certificate.GetFormat();

                    //Output the certificate information
                    Console.WriteLine(certificateInfo + "\n" + "[CertificateFormat]\n " + format);
                }
            }
            Console.ReadKey();
        }
    }
}

PM> Install-Package Spire.Doc

using Spire.Doc;
using Spire.Doc.Documents;

namespace ConvertHtmlToPdf
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // Create an instance of the Document class
            Document doc = new Document();
            // Load an HTML file
            doc.LoadFromFile("Sample.html", FileFormat.Html, XHTMLValidationType.None);

            //Convert the HTML file to PDF format
            doc.SaveToFile("HtmlToPDF.pdf", FileFormat.PDF);
            doc.Close();
        }
    }
}

using Spire.Doc;
using Spire.Doc.Documents;

namespace ConvertHtmlStringToPdf
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // Create an instance of the Document class
            Document doc = new Document();
            // Add a paragraph to the document
            Paragraph para = doc.AddSection().AddParagraph();
            // Specify the HTML string
            string htmlString = @"<h1>This is a Heading</h1>
                                  <p>This is a paragraph.</p>
                                  <ul>
                                    <li>Item 1</li>
                                    <li>Item 2</li>
                                    <li>Item 3</li>
                                  </ul>";

            // Append the HTML string to the paragraph
            para.AppendHTML(htmlString);

            // Convert the document to PDF format
            doc.SaveToFile("HtmlStringToPDF.pdf", FileFormat.PDF);
            doc.Close();
        }
    }
}

using Spire.Doc;
using Spire.Doc.Documents;

namespace ConvertHtmlToXps
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // Create an instance of the Document class
            Document doc = new Document();
            // Load an HTML file
            doc.LoadFromFile("Sample.html", FileFormat.Html, XHTMLValidationType.None);

            //Convert the HTML file to XPS format
            doc.SaveToFile("HtmlToXPS.xps", FileFormat.XPS);
            doc.Close();
        }
    }
}

using Spire.Doc;
using Spire.Doc.Documents;

namespace ConvertHtmlToXml
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // Create an instance of the Document class
            Document doc = new Document();
            // Load an HTML file
            doc.LoadFromFile("Sample.html", FileFormat.Html, XHTMLValidationType.None);

            //Convert the HTML file to XML format
            doc.SaveToFile("HtmlToXML.xml", FileFormat.Xml);
            doc.Close();
        }
    }
}