A signed contract arrives back with a clause that wasn't in the version you sent. The other party insists nothing changed. The signature "looks fine".
PDFs carry evidence of tampering whether the editor knows it or not. You just have to know where to look.
Check the signature panel
Open the PDF in Adobe Reader and look at the Signatures panel. If the document was signed and then altered, you'll see "Signature is invalid" or "Document has been modified since signing".
That's the strongest signal. A valid digital signature means the document content hash matches what was signed.
Inspect the metadata and revision history
PDF metadata records when the file was created and modified. A modification timestamp after the signing date is a red flag.
Some PDFs also carry revision history. Open in the editor and check the document properties for incremental save records. Each save adds a layer; tampering often leaves traces.
Visual comparison against your copy
If you have the version you sent, compare it page by page. Diff tools highlight every text change. Look especially at clauses with monetary amounts, dates, names, and signature blocks — common targets for late-stage edits.
What if there's no signature
Unsigned PDFs have weaker integrity. Without a cryptographic signature, you can only compare against your original copy.
For anything contractual, always sign with a real digital signature using Flint's signing tool. It locks the content and provides an audit trail of any subsequent changes.
FAQ
Can I prove tampering in court?
Forensic PDF analysis can reveal modification history. For litigation, work with a forensic specialist — they have tools that go deeper than reader-level checks.
What if the signature looks valid but the content seems wrong?
Possible the original was already wrong before signing. Compare against your version of record. Signatures only attest to what existed at signing time, not whether that was correct.
Are pasted signature images tamper-evident?
No. A scanned-and-pasted signature has no cryptographic protection. Anyone can change the document and keep the image untouched.
How do I prevent tampering on outgoing PDFs?
Sign digitally and password-protect before sending. The combination prevents both edits and unauthorised viewing.
Tamper-evidence depends on signing in the first place. For your outbound documents, sign properly with Flint so the integrity question is decisive.