.NET PDF Library - Digital Signatures

using Syncfusion.Pdf.Graphics;
using Syncfusion.Pdf.Security;
using Syncfusion.Pdf;
using Syncfusion.Drawing;

// Create a new PDF document
using (PdfDocument document = new PdfDocument())
{
    // Add a new page to the document
    PdfPageBase page = document.Pages.Add();
    // Create PDF graphics for the page
    PdfGraphics graphics = page.Graphics;
    // Load the certificate from a PFX file with a private key
    FileStream certificateStream = new FileStream("PDF.pfx", FileMode.Open, FileAccess.Read);
    PdfCertificate pdfCert = new PdfCertificate(certificateStream, "password123");
    // Create a digital signature
    PdfSignature signature = new PdfSignature(document, page, pdfCert, "Signature");
    // Load the image for the signature field
    FileStream imageStream = new FileStream("signature.jpg", FileMode.Open, FileAccess.Read);
    PdfBitmap signatureImage = new PdfBitmap(imageStream);
    // Set signature information
    signature.Bounds = new RectangleF(new PointF(0, 0), signatureImage.PhysicalDimension);
    signature.ContactInfo = "johndoe@owned.us";
    signature.LocationInfo = "Honolulu, Hawaii";
    signature.Reason = "I am the author of this document.";
    // Draw the signature image on the PDF
    graphics.DrawImage(
    signatureImage, 0, 0);
    // Save the document to a file stream
    using (FileStream outputFileStream = new FileStream("signed.pdf", FileMode.Create, FileAccess.Write))
    {
        document.Save(outputFileStream);
    }
}