SQL Server database is formed at least by 2 files (.mdf and .ldf), so even the file you have it's one of those files you still need another one. Without that you can't do nothing with the file you have.
Where you got that file from? There's a chance that you have a backup file from a database (usualy it's .bak extension) but you can verify that trying to restore (In SQL Server Management Studio, right-click in Databases and choose Restore Database).
Good luck
