SQL Server engine in one place with database files on NAS My office uses accountant programs which run on SQL Server 2008 R2. The SQL Server engine must be installed on one of the laptops (called "server") and the other laptops (called "clients") connect to it via local network. Database files are stored in the same place as the SQL Server engine, so on the "server" laptop. From the security point of view, this is the most ridiculous solution anyone could have so I'm trying to change that.

Is it possible to MOVE only the database files (.mdf) to the NAS which we own, so the SQL Server engine will still run on the "server" laptop but the database will be stored on secured NAS in other place?

Unfortunately it's impossible to install SQL Server on the NAS because it's Synology so it doesn't have MS compatibility (it does have MySQL though).
To be honest, I wouldn't want my database on a NAS as it is most likely accessed throughout the office and it is also very vulnerable as everyone connects to it. Ideally, your SQL database should be hidden in the deepest parts of your network. 

However, I seeing how this doesn't sound like a high end operation, I would see if they can give you the money to get a desktop and install SQL express there to run the database for them. That way all of your clients can just connect to that server from within the network and you have a central point to pull backups from.