PM> Install-Package Spire.PDF

using Spire.Pdf;
    using Spire.Pdf.Security;
    
    namespace AddInvisibleSignature
    {
        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
                PdfSignature signature = new PdfSignature(doc, doc.Pages[doc.Pages.Count - 1], cert, "MySignature");
    
                //Set the document permission to forbid changes but allow form fill
                signature.DocumentPermissions = PdfCertificationFlags.ForbidChanges | PdfCertificationFlags.AllowFormFill;
    
                //Save to another PDF file
                doc.SaveToFile("InvisibleSignature.pdf");
                doc.Close();
            }
        }
    }

Imports Spire.Pdf
    Imports Spire.Pdf.Security
    
    Namespace AddInvisibleSignature
        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
                Dim signature As PdfSignature =  New PdfSignature(doc,doc.Pages(doc.Pages.Count - 1),cert,"MySignature")
    
                'Set the document permission to forbid changes but allow form fill
                signature.DocumentPermissions = PdfCertificationFlags.ForbidChanges | PdfCertificationFlags.AllowFormFill
    
                'Save to another PDF file
                doc.SaveToFile("InvisibleSignature.pdf")
                doc.Close()
            End Sub
        End Class
    End Namespace

using System;
    using System.Drawing;
    using Spire.Pdf;
    using Spire.Pdf.Security;
    using Spire.Pdf.Graphics;
    
    namespace AddVisibleSignature
    {
        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 - 260 - 54 , 200, 260, 110);
                signature.Bounds = rectangleF;
                signature.Certificated = true;
    
                //Set the graphics mode to ImageAndSignDetail
                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\\handwrittingSignature.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("VisiableSignature.pdf");
                doc.Close();
            }
        }
    }

Imports System
    Imports System.Drawing
    Imports Spire.Pdf
    Imports Spire.Pdf.Security
    Imports Spire.Pdf.Graphics
    
    Namespace AddVisibleSignature
        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 - 260 - 54,200,260,110)
                signature.Bounds = rectangleF
                signature.Certificated = True
    
                'Set the graphics mode to ImageAndSignDetail
                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\\handwrittingSignature.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("VisiableSignature.pdf")
                doc.Close()
            End Sub
        End Class
    End Namespace

using Spire.Pdf;
    using Spire.Pdf.Widget;
    
    namespace RemoveSignature
    {
        class Program
        {
            static void Main(string[] args)
            {
                //Create a PdfDocument object
                PdfDocument doc = new PdfDocument("C:\\Users\\Administrator\\Desktop\\VisiableSignature.pdf");
    
                //Get form widgets from the document
                PdfFormWidget widgets = doc.Form as PdfFormWidget;
    
                //Loop through the widgets
                for (int i = 0; i < widgets.FieldsWidget.List.Count; i++)
                {
                    //Get the specific widget
                    PdfFieldWidget widget = widgets.FieldsWidget.List[i] as PdfFieldWidget;
    
                    //Determine if the widget is a PdfSignatureFieldWidget
                    if (widget is PdfSignatureFieldWidget)
                    {
                        //Remove the widget
                        widgets.FieldsWidget.RemoveAt(i);
                    }
                }
    
                //Save the document to another PDF file
                doc.SaveToFile("RemoveSignatures.pdf");
            }
        }
    }

Imports Spire.Pdf
    Imports Spire.Pdf.Widget
    
    Namespace RemoveSignature
        Class Program
            Shared  Sub Main(ByVal args() As String)
                'Create a PdfDocument object
                Dim doc As PdfDocument =  New PdfDocument("C:\\Users\\Administrator\\Desktop\\VisiableSignature.pdf")
    
                'Get form widgets from the document
                Dim widgets As PdfFormWidget =  doc.Form as PdfFormWidget
    
                'Loop through the widgets
                Dim i As Integer
                For  i = 0 To  widgets.FieldsWidget.List.Count- 1  Step  i + 1
                    'Get the specific widget
                    Dim widget As PdfFieldWidget =  widgets.FieldsWidget.List(i) as PdfFieldWidget
    
                    'Determine if the widget is a PdfSignatureFieldWidget
                    If TypeOf widget Is PdfSignatureFieldWidget Then
                        'Remove the widget
                        widgets.FieldsWidget.RemoveAt(i)
                    End If
                Next
    
                'Save the document to another PDF file
                doc.SaveToFile("RemoveSignatures.pdf")
            End Sub
        End Class
    End Namespace