I didn’t manage to use a free tool to sign a PDF document with a certificate, so we’ll use a trial version of Adobe Acrobat Professional.
Our PKCS12 file (with keys and signatures) is imported in our certificate store, so let’s open a PDF document and sign it:
After signing, we notice there’s one issue, our identity is not yet trusted:
Let’s trust ourself:
After validation, Adobe Acrobat tells us our signature is valid: