Server side signing of a digital signature

I'm doing server side dig-sig signing using Word Automation in a multi-user
website environment. Keeping everything thread safe is paramount.
Occasionally the dig-sig processor (app routine) hangs up due to Word error
messages.

I'm looking for someone with a great deal of subject matter expertise in MS
Word digital signatures. There's only one certificate in the pick list so
that's not an issue.

I'm willing to use any version of Word (presently using Word 2003). I need
to make the dig-sig signing bullet-proof. Thanks.