PAdES Explained: The Standard for PDF Signatures

PAdES stands for PDF Advanced Electronic Signatures. It's the ETSI standard (EN 319 142) that defines how a legally valid electronic signature is embedded inside a PDF file. If you've ever signed a PDF and been told the signature is "eIDAS-compliant," what actually made it compliant is PAdES.

What is PAdES?

PAdES specifies the exact structure of a cryptographic signature inside a PDF: what data gets hashed, how the certificate is embedded, where the signature lives in the PDF file structure, and how validators should check it. It builds on top of ISO 32000 (the PDF specification itself) and CMS/CAdES (the underlying cryptographic message format).

Published by the European Telecommunications Standards Institute (ETSI), PAdES is one of three parallel signature standards:

• PAdES — for PDF files (EN 319 142)
• CAdES — for arbitrary binary data (EN 319 122)
• XAdES — for XML documents (EN 319 132)

All three are recognised under eIDAS Regulation (EU) 910/2014 as producing valid electronic signatures. PAdES is the one you meet in practice for contracts, because contracts live in PDFs.

PAdES profiles: B, B-T, B-LT, B-LTA

PAdES defines four baseline profiles, each adding more evidence for long-term validation:

For most B2B commercial contracts, B-T is the practical sweet spot: the signature stays valid past certificate expiry (thanks to the timestamp) without the complexity of embedding revocation data. B-LT and B-LTA matter for regulatory archives and contracts you need to prove signed 10+ years later.

How PAdES compares to CAdES and XAdES

Same underlying cryptography, different containers. CAdES wraps the signature around a raw binary blob (useful for signing anything — images, source code, ZIP files). XAdES embeds signatures inside XML documents (used heavily by EU tax authorities and government-to-government messaging). PAdES embeds the signature inside the PDF structure itself, so the signed file is still a valid PDF that opens in any reader.

Practically: if you're signing a contract, PAdES. If you're signing an XML e-invoice for the Italian SDI or a Peppol document, XAdES. If you're signing a firmware image or a code release, CAdES.

How to verify a PAdES signature

Three ways, in order of trust:

• Adobe Reader — opens any PAdES-signed PDF and shows the signature status (green tick if the certificate chains to a trusted root). Fine for spot-checking, but Adobe's trust store isn't the same as the EU Trust List
• ETSI Signature Conformance Checker — the European standards body's official validator, at signatures-conformance-checker.etsi.org/checker/pades. Free, browser-based, authoritative for eIDAS conformance
• EU DSS demo — Digital Signature Service, the reference implementation from the European Commission. Validates against the EU Trust List directly

All three are free. If you receive a signed PDF and want to be sure, run it through the ETSI checker — it produces a detailed report explaining exactly what was verified and any warnings.

PAdES vs a scanned or drawn signature

A scanned handwritten signature or a JPG dropped onto a PDF is legally an SES under eIDAS — it counts as a signature. But it has none of PAdES' cryptographic properties: any tampering after signing is undetectable, there's no proof the "signer" was actually the person named, and there's no timestamp proving when.

A PAdES B-T signature has all three: cryptographic tamper-evidence, a certificate binding, and a trusted timestamp. Same eIDAS SES tier, dramatically stronger evidence.

eSeal's implementation

eSeal produces PAdES B-T signatures using the EU DSS reference library (the same code the European Commission uses in its own tools). Each signed PDF contains a self-signed certificate for the eSeal signing service plus an RFC 3161 timestamp from a public EU timestamp authority. You can verify any eSeal-signed PDF at the ETSI conformance checker.

For context on where PAdES fits in the eIDAS framework, see our eIDAS guide and the SES/AES/QES explainer.