Thought this would be easy, but it's not...

I'm opening a document with Word through VB automation:

wrdApp.Documents.Open filename, etc.

But I cannot figure out how to tell if someone else already has it opened. Currently, I have to check to see if the caption property has the word "(copy)" in it, but this is obviously not a good long-term strategy. Unfortunately, because this is a 'copy' the read-only property of the doc is set to false, so I can't check that.

Any help appreciated, thanks,
AD