With Windows 7-64bits, Java 1.8.0.151 and Jabref 4.1 when I add a new entry Bibtex (item, book,…), a list of docs are already listed without any operation in the file field (general tab).
However, I can add a new PDF file that is the only property taken into account as an attachment.
Thank you for your help!
Since 4.0 JabRef tries to be intelligent and also displays files that match the file search pattern specified in the preferences. If you want to link the file permanently, you just need to click the small briefcase icon next to it.