Signature Invalid after merging two digitally signed pdf

Sonu kumar Ranjan

Signature Invalid after merging two digitally signed pdf. How we can verify both signatures when we merging a new page after Signature.?

PdfStamper stamper = PdfStamper.CreateSignature(reader, output, '\0', null,true);I had sign pdf passing parameters append mode true. After that Merge another PDF, and Sign. In this case.1st PDF Signature is not verified.

3 Replies

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Leon D5y ago
You can use Spire.PDF library to create and verify digital signatures in PDF. Refer to the following links:

https://www.e-iceblue.com/Tutorials/Spire.PDF/Spire.PDF-Program-Guide/Get-and-Verify-Digital-Signature-in-PDF-with-C-Code.html

https://www.e-iceblue.com/Tutorials/Spire.PDF/Spire.PDF-Program-Guide/PDF-Security/Create-Visible-Digital-Signature-in-PDF-with-C-Code.html
Marvin Reid5y ago
You can use the PDFSignature class provided through the use of the LEADTOOLS SDK to get and set data relevant to a PDF signature. Through this, you can access the properties such as CertificateInfo and State which will provide you with the information of the signature, as well as let you know the validity of it. You can build on the following code to achieve this:
using (PDFDocument document = new PDFDocument(sourceFileName))
{
    // Parse the signatures for all pages
    PDFParsePagesOptions options = PDFParsePagesOptions.Signatures;
    document.ParsePages(options, 1, -1);

    foreach (PDFDocumentPage page in document.Pages)
    {
        // Check PDF for signatures
        if (page.Signatures != null && page.Signatures.Count > 0)
        {
            // Gets the status of digital signature support
            RasterExceptionCode status = PDFDocument.GetDigitalSignatureSupportStatus();
            if (status == RasterExceptionCode.Success)
            {
               // Get info of PDF Signature
                foreach (var pdfSignature in page.Signatures)
                {
                    Console.WriteLine($"The state of the signature: {pdfSignature.State}");
                    Console.WriteLine($"Can this signature be validated: {pdfSignature.CanValidate}");
                    Console.WriteLine($"Certificate Info:");
                    foreach (var info in pdfSignature.CertificateInfo)
                    {
                        Console.WriteLine($"\t{info}");
                    }
                }
            }
        }
   }
}
https://www.leadtools.com/help/sdk/v21/dh/pdf/pdfsignature.html
Jay Krishna Reddy5y ago
https://www.syncfusion.com/blogs/post/create-validate-pdf-digital-signatures-csharp.aspx

https://www.textcontrol.com/technologies/pdf/?gclid=Cj0KCQjwpf2IBhDkARIsAGVo0D2lMGrm6aUGZ6dPFqyGHEq1ImZwTYrdkyXf21uTOTQCvn1TkB3gH2MaAji5EALw_wcB

Hope the above links helps