Adobe Acrobat XI User Manual download pdf (Page 405)

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Electronic signatures

Last updated 1/14/2015

For more information about signature warnings and valid and invalid signatures, see the Digital Signature Guide at

www.adobe.com/go/acrodigsig.

You assess the validity of a Digital Signature and Timestamp by checking the Signature Properties.

1 Set your signature verification preferences. For more information, see Set signature verification preferences.

2 Open the PDF containing the signature, then click the signature. The Signature Validation Status dialog box

describes the validity of the signature.

3 For more information about the Signature and Timestamp, click Signature Properties.

4 Review the Validity Summary in the Signature Properties dialog box. 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 in the Signature Verification

Preferences dialog box (Preferences > Signatures > Verification: More). Acrobat and Reader display an alert message

when validating signatures with expired timestamp.

5 For details about the signer’s certificate, such as trust settings or legal restrictions of the signature, click Show Signer’s

Certificate in the Signature Properties dialog box.

If the document was modified after it was signed, check the signed version of the document and compare it to the

current version.

Remove a digital signature

You cannot remove a digital signature unless you are the one who placed it and you have the digital ID for signing it

installed.

❖ Do one of the following:

• To remove a digital signature, right-click the signature field and choose Clear Signature.

• To remove all digital signatures in a PDF, choose Clear All Signature Fields from the options menu in the

Signatures panel. (To open the Signatures panel, choose View > Show/Hide > Navigation Panes > Signatures.)

View previous versions of a digitally signed document

Each time a document is signed using a certificate, 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 digital 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.

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Adobe Acrobat XI User Manual Page 405

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