PDFTron 数字签名

Question

I'm currently working on a Digital Signature project in Python which can create digital signature on PDF documents and verify them. I was able to add a single digital signature to PDF Files using the code below:

PDFNet.Initialize()
doc = PDFDoc(pdf_path)
page1 = doc.GetPage(1)

# Create signature field
sign_field = doc.CreateDigitalSignatureField("Signature")
widgetAnnot = SignatureWidget.Create(doc, Rect(0, 0, 100, 100), sign_field)
page1.AnnotPushBack(widgetAnnot)
sign_field.SignOnNextSave(pkcs12_path, "")
# Save file
output_path = get_only_path(pdf_path) + "output.pdf"
doc.Save(output_path, SDFDoc.e_incremental)

PDFNet.Terminate()

I was also able to verify the document with the code below:

    # Get certificate
    dsfield_iter = doc.GetDigitalSignatureFieldIterator()
    while dsfield_iter.HasNext():
        sign_field = dsfield_iter.Current()
        cert = sign_field.GetSignerCertFromCMS()
        dsfield_iter.Next()
    
    # Save certificate for verification
    cert_path = get_only_path(pdf_path) + "certificate.cer"
    with open(cert_path, "wb") as cer:
        # cert.GetData() return DER format
        cer.write(cert.GetData())

    # Verifying signature
    opts = VerificationOptions(VerificationOptions.e_compatibility_and_archiving)
    opts.AddTrustedCertificate(cert_path)
    result = doc.VerifySignedDigitalSignatures(opts)

However, I have a problem. I want multiple people to be able to sign on the same document with their self signed certificate in different signature fields and also able to verify the document. I used my code for the same process but was unable to verify the signature after more than one people sign on it. I would like to get help on this, please kindly share your thoughts:)

Answer 1

Yes you can add multiple Signature Fields and Sign them using PDFTron SDK. Just repeat the SignOnNextSave code you had above, and always make sure to save using e_incremental .

Note though that currently PDFTron Validation would fail once two or more signatures added, as this would strictly speaking violate what the PDF specification describes for default behavior. Though I checked with Adobe Acrobat at least and it was fine with 2+ signatures, so at least Adobe appears to be doing something proprietary and non-standard. I cannot say about other vendors, if that is important for you.