How to make sure that your Office document has a valid digital signature in 2007 Office products and in Office 2003

This article describes:

• How to make sure that a digitally signed Microsoft Office document has a valid digital signature.
• How to make sure that a document was not tampered with after the document was originally digitally signed.

To confirm that a digitally signed Office document came from a trusted source, and that the document was not modified after it was digitally signed, view the document's digital signature. 2007 Office products and Office 2003 support digital signatures on documents.

When you receive a digitally signed document, it is a good idea to check the digital signature for authenticity. For performance reasons, Office does not automatically check the authenticity of a digital signature when you open a document. To determine whether a document has an authentic digital signature, follow these steps as appropriate:

2007 Office products

1. Open the digitally signed Office document.
2. Click the Microsoft Office button.
3. Click Prepare, and then click View Signature.

To view details about a particular certificate, click the down arrow on the certificate to be viewed in the Signatures task pane, click Signature details, and then click View to view the details of the certificate.

Office 2003

1. Open the digitally signed Office document.
2. On the Tools menu, click Options.
3. Click the Security tab, and then click Digital Signatures. The Digital Signature dialog box contains information that includes the signer's name, the provider of the signer's digital signature, and the date when the document was digitally signed.
4. To view details about a particular certificate, click the name of the signer, and then click View Certificate.

You may also click the Digital Signature icon in the Status bar.

A valid certificate has the image of an unblemished certificate in its upper-right corner. A certificate with problems shows the image with a red X.

The following actions may cause a digital signature to become not valid:

• Changes are made to a document that cause recalculation. For example, if changes occur to volatile functions, fields or queries that are set to automatically update, and VBA macros that change the file when they are run, the digital signature may become not valid.
• Changes are made to a document, and then the Undo feature is used.

For more information about how to determine whether a digital signature is valid, and for detailed information about the contents of a digital certificate, visit the following Microsoft Web site:

A feature in Word 2003 informs you if there are signs of tampering with a digital signature. If there are signs of tampering, such as with a hexadecimal (hex) editor, you receive the following error message before the digital signature dialog opens: For more information about digital signatures, see the Office Help documentation.

To learn more about digital signatures and certificates, visit the following Microsoft Web sites: