Microsoft's server uses a single sign on so you set up accounts on the server and that's the password. You can extend rights to that folder or revoke as needed.
Remember I know this system. It's a bad design if the database file is directly exposed like that. For years we moved to SQL to remove direct access to the file and SQL provides a granular access you are asking for.
-> Until then you backup daily, weekly monthly like you were taught.
My company uses MS Access '07, with the data stored on a shared back-end, and accessed by each user through their front-end application. However, since the back-end file has to be accessed by everyone's front-end, it is left vulnerable to attack, should someone wish to destroy it.
Is there a way to password protect it if someone were to try to open the back-end file, but that would still allow unfettered access by the front-end application?