What is the proof file (audit trail) and what does it contain?

The proof file (or signature certificate / audit trail) is the document that records the whole signing process. It typically gathers:

• the signers' identities and their verification method,
• a timestamp for each action (opening, viewing, signing),
• IP addresses,
• the digital fingerprint of the signed document,
• the eIDAS signature level used.

It's generated automatically and attached to the signed document. It's the exhibit you produce in a dispute to prove who signed what, when and how.