How to apply digital signature to PDF with multiple pages in ASP.NET wit C#?

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C#

ASP.NET

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itextsharp

I want to apply Digital Signature to PDF with multiple pages in asp.net wit c#. I am using Itextsharp dll.
I tried using pdfsignature class and was able to set the digital sign, But I need to apply multiple signatures to the PDF. I am able to apply only to a single page even on clearing a new object for pdfsignature class.

What I have tried:

PdfSignatureAppearance sap = st.SignatureAppearance;

           sap.SetCrypto(this.myCert.Akp, this.myCert.Chain, null, PdfSignatureAppearance.WINCER_SIGNED);
           sap.Reason = SigReason;
           sap.Contact = SigContact;
           sap.Location = SigLocation;
           string SourcePDFFullPath = @"F:\Test.pdf";
           PdfReader pdfReader = new PdfReader(SourcePDFFullPath);

PdfSignatureAppearance sap1 = st.SignatureAppearance;

           sap1.SetCrypto(this.myCert.Akp, this.myCert.Chain, null, PdfSignatureAppearance.WINCER_SIGNED);
           sap1.Reason = SigReason;
           sap1.Contact = SigContact;
           sap1.Location = SigLocation;
           string SourcePDFFullPath = @"F:\Test.pdf";
           PdfReader pdfReader = new PdfReader(SourcePDFFullPath);


               sap.SetVisibleSignature(new iTextSharp.text.Rectangle(100, 100, 250, 150), 1, null);
               sap1.SetVisibleSignature(new iTextSharp.text.Rectangle(100, 100, 250, 150), 2, null);