Glossary
What is a trusted timestamp?
Short answer
A trusted timestamp proves a document existed in a given form at a given moment, using a clock you do not control. The signing software sends the document's hash to a timestamp authority, which returns a token signed with its own key, following RFC 3161. Sign PDF's seal carries a timestamp from DigiCert's timestamp authority, so the signing time does not rest on our own servers' clock.
Updated 25 October 2026
- Trusted timestamp
- A trusted timestamp is a token issued by an independent timestamp authority, under the RFC 3161 protocol, that binds a document's hash to a specific date and time and is signed by the authority so it cannot be backdated.
How RFC 3161 timestamps work
RFC 3161, the Internet X.509 Public Key Infrastructure Time-Stamp Protocol, was published by the IETF in August 2001. The client hashes the data and sends only the hash to a Time Stamping Authority (TSA). The TSA adds the current time from a reliable source, signs the hash and time together with its certificate, and returns the token.
The TSA never sees the document itself. Anyone can later check the token: recompute the document hash, confirm it matches the one in the token, and check the TSA's signature.
Why an independent clock matters
If a platform stamps documents with its own server time, a sceptic can ask whether that time could have been set differently. An independent authority removes the question. Its business depends on keeping accurate time and protecting its signing keys.
Timestamps also extend a signature's life. If a signing certificate later expires or is revoked, a timestamp shows the signature was made while the certificate was still valid.
Timestamps under eIDAS and PAdES
eIDAS covers electronic time stamps in Articles 41 and 42. A qualified electronic time stamp, from a qualified trust service provider, enjoys a presumption of the accuracy of the date and time it shows. A non-qualified timestamp is still admissible as evidence.
In PAdES, adding a timestamp to a signature moves it from the B-B level to B-T.
How Sign PDF timestamps documents
Each completed Sign PDF document is sealed with a digital signature carrying an RFC 3161 timestamp from DigiCert's timestamp authority. The individual signer events in the certificate of completion are recorded in UTC from our servers, and the seal timestamp independently fixes when the finished file existed in that form. We do not describe it as a qualified eIDAS time stamp.
Questions people ask
Does the timestamp authority see my document?
No. Only a hash of the document is sent. The hash cannot be turned back into the document.
What time zone are timestamps in?
RFC 3161 tokens use UTC (generalised time). Sign PDF's certificate of completion also records signer events in UTC.
Is a trusted timestamp the same as a postmark?
It plays a similar role: an independent third party records when something existed. Unlike a postmark, it is tied to the exact content by a hash.
How do I see the timestamp on a signed PDF?
In Adobe Acrobat Reader, open the signature panel and expand the signature details. It shows whether the signature includes an embedded timestamp and from which authority.
Upload a document and watch the boxes land
See every signature, initial and date box placed before you sign up. Sending starts at $5 a month, monthly, cancel any time.
Upload a document