Hey there,
As nobody else oferred any help I eventually got a Microsoft Quick Assist card and after chatting to them (though not actually getting a resolution yet) I have found a way to get pretty much what I wanted.
First step was to edit the form to Include a "File Attachment" button, which I didn't know was available before, I did not decode/recode anything and only limited users to attaching PDF files.
Secondly, I published the form to a server accessable to all users.
Thirdly, I edited the Hyperlink on the Office button (see previous links on how to build that) to point at the form on the server.
It seems to work pretty well and if I could just remove all the warning popups and send confirmation requests I'd be in business.
thanks for listening (if not answering...)
M.
ps. I still have nothing on .fdm extensions.