Using the default notes functionality in GP you can attach files to notes. If you attach multiple files they get added on top of each other. If you’re not paying attention and you add multiple files it can look like only one has been added because they are all sitting on top of each other. Just grab the top one and drag it off to side to see multiple files.
Weekly Dynamic: Attaching Notes
Archived post from 2013. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.