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How to verify a signed contract PDF

A signed contract is only as good as the question nobody asks: is the signature real, and does it cover the document you're holding? Most disputes over a signed PDF don't turn on a forged scrawl — they turn on a page or a clause added after the signature, or an e-signature that records far less than people assume. Both are checkable.

Know which kind of signature you have

There are two different things called a signature on a PDF, and they prove different amounts.

A digital signature is cryptography embedded in the file. It can prove, with math, that the signed bytes have not changed and that they were sealed by the holder of a particular certificate. This is the strong kind, and it is the one a file examination can verify directly without asking anyone.

An e-signature platform signature (the "sign here" services) usually records consent — a typed or drawn signature image plus an audit trail held by the platform. The proof lives with the platform, not in the file, so the PDF alone often can't confirm much. Some platforms also apply a real digital signature; that is the case worth confirming.

The three checks

1. Is a digital signature present, and is it valid? A valid signature means the bytes were sealed by the certificate's holder. Check whose certificate it is — a self-signed certificate carrying a borrowed name is the soft attack here, so the signer identity matters as much as the validity.
2. Does the signature cover the whole file? This is the one that catches real trouble. A signature seals a specific range of bytes. If content was appended afterward — an added page, a changed number — the signature covers the earlier version, not the document in your hands. That gap is detectable with certainty.
3. What does the metadata say happened after signing? Modification dates and revision history can show re-saves and edits layered on after the signing event, which is your cue to compare against the originally signed copy.

What to do with what you find

If the signature is valid and covers the whole file, you have strong cryptographic ground to stand on. If content was added after signing, separate the signed version from the later additions before you act, and ask the other party for the originally signed copy. If the "signature" is only an e-signature image, treat the platform's audit trail — not the PDF — as the record, and request it if the contract is contested.

FAQ

Can a digital signature be forged?

Forging the math requires the signer's private key, which is impractical. The realistic attacks are softer: a self-signed certificate using someone's name, or content appended outside the signed range. Both leave evidence in the file, which is exactly what an examination reads.

Is a typed or drawn e-signature legally binding?

Often yes, depending on jurisdiction and context — but legal weight is a separate question from what the file can prove. The image and the platform's audit trail are the record; the PDF by itself usually can't verify them, so keep the platform's completion certificate.

Someone added a page after I signed. Can that be detected?

Frequently, yes. If the document was digitally signed, content added after the signature falls outside the signed byte range and is detectable. If it was unsigned, modification records and version comparison are the route — comparing the two versions can show exactly what changed and which came first.