What is Tamper-Evident?
A property where any post-signing change to a document is immediately detectable through a hash mismatch.
A tamper-evident signed document carries a cryptographic seal — a hash of the document at signing time — that lets anyone verify whether the document has been altered since. Open the signed PDF, recompute the SHA-256, compare against the hash on the audit certificate; if they match, the document is untouched. If they don't, even a single byte has changed. PDF Verified publishes the hash on the audit certificate and on the public /verify QR page so verification is one click away.
Tamper-evident vs tamper-proof
No digital document is truly tamper-proof — anyone can edit a PDF in Acrobat. But tamper-evidence means the change is immediately visible: the hash on the audit certificate no longer matches the live document. Tampering becomes self-defeating.
PKI seals
A stronger form: the signed PDF carries an embedded PKI signature (an Adobe-recognized digital signature). Adobe Reader will display a yellow or red banner the moment any byte changes. PDF Verified adds embedded PKI seals on Business Plus.
In court
In ESIGN/eIDAS jurisdictions, a tamper-evident hash on a contemporaneous audit certificate is admissible evidence of document integrity. Combined with the audit trail, it answers the two questions a court asks: who signed, and has anything changed since.