This is an old question, but if someone comes here later (like me), this may help:
If you cannot restore the backup and you have both files, you can restore the database by going to Tasks > Restore > Database and clicking From Device .
Choosing Database in the menu is an important point. It seems to me impossible to restore a database divided into several files using the Files and Filegroups .
Thanks to Hamid Sirat's answer in the link posted earlier by ughai ( here ) for this solution.
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