adding on ...
I usually hang directories under the back-end location, organized under a Files folder -- then even if the path to the back-end is referenced differently for various users, the application can get the back-end path from the connect string of one of the linked tables. Then a relative path to the top level path for files can be used. In my databases, if a path starts with "\", it's a relative path to CurrentProject.Path\Files, not absolute
Generally then, when a file is chosen, it is either moved or copied to this area under the back-end.