Add Signature to PDF


we are trying to add a Signature to a PDF, the PDF is generated, but it comes with a warning “at least 1 signature is invalid”. we cannot add the certificate to the trusted list.
The topic is very similar to At least one signature is invalid message - #3 by Jaehoon

After we first open the PDF, We performed following steps:
Untitled.png (4.6 KB)

  • Right Click over Signatures and goto Signature Properties

  • Press Show Signer Information button in popup

  • Noting happens


using (Document document = new Document(docStream))
using (PdfFileSignature signature = new PdfFileSignature(document))
Signature sing = new PKCS7Detached(@“c:\path\to*.pfx”, password);
signature.Sign(1, false, new System.Drawing.Rectangle(10, 10, 200, 200), sing);
// Save output PDF file


I request you to share a sample application so that we may try to reproduce the same on our end.

hi Fayyaz,

I got it to work.
I was encrypting the PDF after I had signed it.
and that breaks the signature.

so advice for every one, if you are sinning a PDF, that is the last thing you do.


It’s good to hear that things are fine on your end.