You are probably used to having a single-file database which you can move around as much as you want. But, your database has grown too big and now you need a multi-file database. Paths to the secondary files are absolute and stored in the header page of the first database file. If you need to move those files, it is recommended that you backup the database and restore at new location. However, if you really, really need to copy them around, you can use freeware tool GLink by Ivan Prenosil: