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SharePoint 2007 document libraries appear to be writing hidden data
into Word documents that causes the digital signatures in the document
to become invalid (because the document appears to have been modified).

Specifically, digitally signed documents authored/signed with Word 2003
become invalid. However, digitally signed documents authored/signed
with Word 2007 do not - they are able to maintain their validity.

Here is a sample of actions that can cause a Word digital signature to
become invalid:

· Uploading a digitally signed document from the desktop into a
SharePoint 2007 document library.
· Starting a workflow on a document library, if it is the first time
that workflow has been used on the library, will invalidate the digital
signatures of every document in the library.
· Editing the Association of a workflow template with a document
library will invalidate the digital signatures of every document in the
library.
· Adding new columns to the document library will invalidate the
digital signature of every document in the library.
· Editing the properties of a document will invalidate the digital
signature of the document.
· Events that write data to a property of a document when it is
saved/updated will invalidate the digital signature of the document.

We are hoping someone can help us with this issue. We are using a
Microsoft Partner's digital signature solution in our software and
their signatures are becoming invalid too during the course of
interacting with SharePoint 2007 document libraries. They are looking
for advice on what part of the document SharePoint is changing that is
causing their signatures to invalidate.