You edited a signed PDF — added a comment, changed a date, whatever. Now the signature shows invalid. The document looks the same but the signature warning is loud.
What's actually going wrong
Signatures cryptographically commit to the file's exact state at signing. Any modification — even microscopic — invalidates the commitment. This isn't a bug; it's the entire point of digital signatures.
The signature isn't broken in any repairable sense. The fact of modification is recorded permanently.
The quick fix
If you have authority and the signer's trust, re-sign yourself using Flint's sign tool. The new signature is yours, not the original signer's, and the file now has your authentication rather than theirs.
If the original signature mattered (legal contract, official document), ask the original signer to re-sign. You can't restore their signature; only they can produce a new valid one.
If that didn't work
For documents where signature integrity is essential, the edit shouldn't have happened. Going forward, always work on unsigned copies and sign only the final version.
For some legal contexts, broken signatures aren't recoverable in any way — the document is officially invalidated. Consult counsel for legally significant cases.
Prevent it next time
Treat signed PDFs as final. Maintain an unsigned working copy alongside the signed final. Sign only after all edits are complete and reviewed.
FAQ
Can a broken signature be fixed?
Cryptographically, no. The signature commits to a specific file state; modification changes that state irrevocably. Re-signing produces a new signature, not a restored one.
Does the warning ever go away on its own?
No. Once a signature is invalidated by modification, the file carries that invalidation permanently. Re-signing or accepting the warning are the options.
Can I edit just metadata without breaking the signature?
Most viewers will allow some metadata edits without invalidating signatures, but the rules vary. Safest assumption: any change breaks signatures.
Why is editing signed PDFs so restrictive?
Signatures exist to prove the file wasn't changed after signing. If edits didn't invalidate signatures, signatures couldn't prove anything. The strictness is the value.
Broken signatures stay broken. Re-sign via Flint if appropriate, or accept the modification record.