Backup/restore kepubs on glo?

I've got some kepubs on my glo that I cant get the ade-epub version.
I'd like to back them up (just in case). And be able to restore them.

This question could equally be, How does syncing work?
If I have kepubs on the reader that aren't on kobo-desktop will desktop download from the reader (creating a backup)? OR (worse) Will desktop tell the reader to delete the unknown kepubs? I've never used kobo-desktop.