如何在C＃中将数字图章添加到现有的PDF文件中？

Question

我有一个PDF文件的文件，需要在文件的特定位置加上数字印章。我把邮票放在档案中，但我想把邮票放在档案的特定位置。

这是我的代码

protected void btnCreatePDF_Click(object sender, EventArgs e)
{
    String cert = "C:/Users/arehman.SHERPC-1009/Desktop/New folder (3)/iTextSharpSign_TemporaryKey.pfx";
    PdfFileSignature pdfSign = new PdfFileSignature();
    pdfSign.BindPdf("C:/Users/arehman.SHERPC-1009/Downloads/FormalUndertakingForm (5).pdf");
    //create a rectangle for signature location
    System.Drawing.Rectangle rect = new System.Drawing.Rectangle(50, 50, 100, 50);
    //set signature appearance
    pdfSign.SignatureAppearance = "c:/users/arehman.sherpc-1009/documents/visual studio 2010/Projects/TestApp/TestApp/Images/sig55.png";
    //create any of the three signature types
    PKCS1 signature = new PKCS1(cert, "edge123"); // PKCS#1 or
    signature.ShowProperties = false;
    //PKCS7 signature = new PKCS7("test.pfx", "password"); // PKCS#7 or
    //PKCS7Detached signature = new PKCS7Detached("test.pfx", "password"); // PKCS#7 detached
    pdfSign.Sign(2, true, rect, signature);

    //save output PDF file
    pdfSign.Save("C:/Users/arehman.SHERPC-1009/Downloads/Pdf/output.pdf");            
}