PAdES
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Definition
PAdES (PDF Advanced Electronic Signatures) is the European standard, ETSI EN 319 142, for embedding cryptographic digital signatures inside PDF files so that any later modification of the document is detectable by any standard PDF reader.
PDF was always a good envelope for signed documents; PAdES made it a tamper-evident one. The standard, maintained by ETSI and recognized under eIDAS, defines exactly how a digital signature lives inside a PDF's structure so that Adobe Acrobat, browser viewers, and verification tools can all check the same seal the same way.
What a PAdES seal proves
Two things, mathematically: who sealed the document, via the X.509 certificate embedded in the signature, and integrity, since the signature covers a byte-range hash of the file, so changing anything after sealing breaks verification visibly. Profiles add longevity features, with PAdES-T adding a trusted timestamp and PAdES-LTA archival data so the seal stays verifiable decades later, even after certificates expire.
PAdES vs a drawn signature in the PDF
An image of a signature pasted on page 4 is decoration; anyone with an editor can move it to a different contract. A PAdES seal is structural: it's computed from the document's bytes, so it can't be lifted onto other content, and any edit, even a single character, flips the document to 'modified since signing' in every compliant reader.
How Sign Sail uses it
When an envelope completes, Sign Sail generates the final PDF with the signatures and the audit-trail evidence, then applies a PAdES digital seal with its signing certificate. Open the file in any PDF reader with signature support and you can verify the document hasn't been touched since completion. The seal is on every plan, not an enterprise add-on.
↗ · Common questions
Do my signers need certificates for PAdES?
No. The platform applies the seal with its own certificate after signing completes; signers just sign normally. The seal proves the completed document's integrity. Signer-held certificates only enter the picture for EU advanced or qualified signature tiers.
How do I verify a PAdES-sealed PDF?
Open it in a reader with signature verification, like Adobe Acrobat, and check the signature panel. It will show who applied the seal, when, and whether the document has been modified since. No special software or account with the issuing platform is needed, which is the point of using a standard.
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See it in a real signature.
Every Sign Sail plan, the free one included, captures this evidence on every signature.