PAdES

PAdES, or PDF Advanced Electronic Signatures, is a set of specifications developed by the European Telecommunications Standards Institute (ETSI) to enable legally robust digital signatures within PDF documents in support of EU eIDAS regulations. The aim is to provide signatures whose validity can be demonstrated over an extended period, even as cryptographic standards, certificate authorities, and device availability change.

A PAdES signature applies to the PDF signature mechanism defined in the PDF standard and typically includes the signer's certificate and certificate chain, the signing time, and validation data such as revocation information (OCSP responses or CRLs). It may also incorporate a trusted timestamp from a Time Stamping Authority (TSA). By embedding or reliably linking this data to the PDF, PAdES facilitates long-term verification of signatures independent of the signer's original signing environment.

To support long-term validity, PAdES outlines how to preserve and manage verification information so that a signature can be validated long after its creation. This can involve including archival data, updating references, and enabling extended forms of long-term validation that comply with eIDAS expectations for non-repudiation and legal acceptance.

PAdES interacts with the PDF format (ISO 32000-1/2) and the CMS/PKCS#7 signature framework. It is commonly implemented through signature baselines that specify the presence of timestamps and revocation data to ensure verifiability over time. Practical use requires compatible signing and viewing tools that support PAdES features and trusted trust anchors.