Operation Manual

236
USING ACROBAT X STANDARD
Digital signatures
Last updated 10/11/2011
Validate a timestamp certificate
Review the Validity summary section on the Summary tab of the Signature Properties dialog box for the validity status
of a timestamp certificate. The summary might display one of the following messages:
Signature date/time are from the clock on the signer's computer The time is based on the local time on the signer’s
computer.
Signature is timestamped The signer used a timestamp server and your settings indicate that you have a trust
relationship with that timestamp server.
Signature is timestamped but the timestamp could not be verified Timestamp verification requires obtaining the
timestamp server's certificate to your list of trusted identities. Check with your system administrator.
Signature is timestamped but the timestamp has expired Acrobat and Reader validate a timestamp based on the
current time. This message is displayed if the timestamp signer's certificate expires before the current time. To let
Acrobat or Reader accept an expired timestamp, select Use Expired Timestamps from the Digital Signature Advanced
Preferences dialog. To display the Digital Signature Advanced Preferences dialog, choose Security from the Categories
pane in the Preferences dialog, and then click Advanced Preferences. Acrobat and Reader display an alert message
when validating signatures with expired timestamp.
To validate a signature that contains a timestamp:
1 Click the Signatures button in the navigation pane, select the signature, and choose Validate Signature from the
options menu .
2 Click the Signature Properties button in the Signature Validation Status dialog box.
3 In the Signature Properties dialog box, click the Date/Time tab to view the timestamp authority, and then click the
Show Certificate button. This button appears in the Date/Time tab only if the signer used a timestamp server.
4 In the Certificate Viewer, click the Trust tab to determine if the timestamp certificate is trusted. If it isn’t trusted by
Acrobat but you trust it, click Add To Trusted Identities. If a certificate for the timestamp server isn’t listed, request
one from the signer.
More Help topics
“Securing documents with certificates” on page 203
View previous versions of a signed document
Each time a document is signed, a signed version of the PDF at that time is saved with the PDF. Each version is saved
as append-only and the original cannot be modified. All signatures and their corresponding versions can be accessed
from the Signatures panel.
1 In the Signatures panel, select and expand the signature, and choose View Signed Version from the option menu .
The previous version opens in a new PDF, with the version information and the name of the signer in the title bar.
2 To return to the original document, choose the document name from the Window menu.
Compare versions of a signed document
After a document is signed, you can display a list of the changes made to the document after the last version.
1 In the Signatures panel, select the signature.
2 Choose Compare Signed Version To Current Version from the option menu .
3 When you’re done, close the temporary document.