If you need to backup your database, you have to use the functionallity provided by SQL-Server. To do this, you need administration rights in the database you want to create a backup. Open the Enterprise Manager for SQL-Server, choose the database and detach it from the server as shown in the image below.

After detaching the database, you can store a copy of the ..._Data.MDF File to keep it as a backup.

After storing the backup you have to attach the database.

A dialog will appear where you have to select the original database file in your directory.