Sorry for the delayed response and inconvenience caused. Acrobat provides users with the capability to add a document timestamp to a PDF without also requiring an identity-based signature. A timestamp server is required to timestamp a PDF. See: Acrobat Help | Acrobat User Guide
A timestamp assures the authenticity and existence of a document at a particular time. These timestamps are compliant with the timestamp and revocation features described in Part 4 of ETSI 102 778 PDF Advanced Electronic Signatures (PAdES) standard.
For detailed information, please refer to Eliminating the Pen…One Step at a Time: PAdES PDF Advanced Electronic Signature Standard Released for EU Link: http://blogs.adobe.com/security/2009/09/eliminating_the_penone_step_at.html
You may also refer to Validating digital signatures, Adobe Acrobat
Feel free to update this discussion for any further assistance.