I've been asked to distribute electronic certificates (they were originally paper), in a PDF format, but I'd like to sign them with gpg or something similar so users can upload them to my site to check that they've not been handed a fake copy.So, I'd like to sign a PDF file (transparently, the user doesn't need to know about anything) and check if its valid.
Sign a PDF file to verify integrity and validity
pdf;gpg;signature
You can do it with a separate signature file.Sign the Document:% gpg --output doc.pdf.sig --detach-sig doc.pdfDistribute doc.pdf and doc.pdf.sigVerify the Document:% gpg --verify doc.pdf.sig doc.pdf