Protect SQL Server Express data file I need to protect a Microsoft SQL Server 2008 data file (.mdf) against restoring/attaching on another machine. I'm aware of TDE or Transparent Data Encryption but unfortunately this option is not available in Express version. Any other way to protect the database? 

Thanks
You cannot do encryption with express edition but can you can do it by other way 

or file encryption only. For more reference follow http://sqlmag.com/database-security/sql-server-encryption-options.