Yes, a DocStar reference is completely different than a Windows reference. There are two files to populate when doing Attachments: XFILEREF and XFILEATTACH. DMT has the attachment part done by object (search for Attach in DMT menu on the left). I would manually attach a file in DocStar and look at the format. It looks like the DocStar GUID;patch info if I recall. So the tricky part is you need to know that number. Also, you’ll need to know the meta data to get the various linked tables (SONum, PONum, etc.)
Loading files into DocStar in batch is trivial. Linking them after the fact back into Epicor, not trivial. Unless something has changed or a load utility was created that I’m not aware of.