Restoring an SQL Server 2012 MDF to SQL Server 2008
Your only avenue is to export the database and then import it back on SQL 2008. SSMS has an Export/Import Wizard you can give a shot. Other tools exists from 3rd party vendors like Red Gate's SQL Compare to copy the schema and Data Compare to copy the data. I'm sure there are more. The gist of it that you need to go through some sort of export/import, SQL Server does not support any downgrade path for the MDF format. Obviously, you must not had rely on new SQL Server 2012 features like columnstores.