Make a backup of the database, and specify the WITH MEDIAPASSWORD = ‘YourPassword’ parameter. This will secure the backup file with a password. This method will be removed from a future version of SQL Server.
However it isn’t had to bypass this password. You are better off to encrypt the database using Transparent Data Encryption, which requires that the user has the encryption key in order to restore the database. (This requires SQL Server 2008 and higher.)