Well, from now on, you can solve this little problem thanks to OpenedFilesView, a useful app that lists all of the files currently being used by the system.
OpenedFilesView gives its users a complete list of each and every one of the files being used. It also provides certain characteristics, such as where the file is found, its specs, size, date it was made/changed, the process it's a part of (and that process' file path), etc.
This way, you can figure out exactly which process corresponds to which document, and whether or not you can get rid of it.
You can also finalize any process, open a window with information on the file, or export the list in HTML format, all from the program's interface