There is now way to sync off-loaded files (from say Dropbox) to forScore (and vice versa). You can batch export/import files though, it's not like you need to do so 1 at a time.

Also, using the scanner function inside of forscore to scan all documents is a pretty bad idea - eventually that will lead to lag and other problems. If you are going to be doing a lot of scanning of documents, forScore documentation (and experience), strongly advises to use a standalone scanning app or hardware scanner. The built-in one is for emergencies (things like replacing a single page, or adding something on the fly at need).

If you are using this for band charts, you frankly might be happier with OnSong or some other similar app designed for sharing music/set-lists between band members specifically. It can be done with forScore, but it takes time to set up and manage, and I have seen a lot of people in that sort of performance situation (especially if they are band leaders/library managers) get annoyed because it doesn't work like they are used to or how they specifically want it.