How to make sure that your Office XP document has a valid digital signature

This article describes how to:

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

You can confirm that a digitally signed Office document came from a trusted source, and that the document was not modified after it was digitally signed. You can do this by checking the document's digital signature. Digital signatures on documents are supported in Office XP.

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

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

When a signature IS VALID, you will see the following dialog box. Note that the text does not appear dimmed for Signer, Digitial ID Issued By, and Date, which is under the list titled "The following have digitally signed this document":


When a Signature is NOT VALID, you will see the following dialog box. Note that the text appears dimmed for Signer, Digitial ID Issued By, and Date, which is under the list titled "The following signatures will be discarded when saving changes to the document":


The following actions may cause a digital signature to become invalid:

• When changes are made to a document that cause recalculation. This includes volatile functions, fields or queries set to automatically refresh, and VBA macros that change the file when they are run.
• When changes are made to a document, and then the Undo feature is used.

For more information about how to determine if a digital signature is valid, and for detailed information about the contents of a digital certificate, visit the following Microsoft Web site: For additional information about digital signatures, see the Office Help documentation.

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