Date and time are by default included with a digital signature. A digitally-authorized time stamp indicates that the contents of any data file existed at that time and have not changed since then. A time stamp is usually fetched from a third-party time stamp authority associated with its trusted certificate.
If you have configured a time stamp authority server, the time stamp will appear on the Date/Time tab of the Signature Properties dialog box. You can select the certificate of the time stamp authority and add it to your trusted identities list. If no time stamp is successfully retrieved, the date and time from your local computer will be used.
To time stamp signatures of PDF documents
Choose Security > Sign and Certify > Time Stamp for the Time Stamp Server dialog box. It lists all services you have chosen Click Add to place a new service. Choose one to be used for the current document.
To manage Time Stamp authorities
Choose Security > IDs and Certificates > Manage Digital Identities.
Select Time Stamp Server in the left-side window.
If there are existing time stamp authorities, you can edit or remove them.
Select a time stamp authority and click the Set as Default button. Next time you sign a document, it gets time stamped by the specified time stamp authority.
To add a new time stamp authority
Click the Add button in the Time Stamp Server dialog box or the Security Settings dialog box described above.
In the Add Time Stamp Server dialog box, enter the time stamp authority name and its URL. If the Time Stamp Server requires logging on, enter your user name and password, and click OK.