I have a file with .bak
extension.
How can I import this date to a database in SQL Server?
Instead of choosing Restore Database..., select Restore Files and Filegroups...
Then enter a database name, select your .bak file path as the source, check the restore checkbox, and click Ok. If the .bak file is valid, it will work.
(The SQL Server restore option names are not intuitive for what should a very simple task.)