A manual for restoring an MS SQL Server database comprised of several files
How to restore a Microsoft SQL Server database that consists of several files?
If your database consists of several files (a main MDF file and additional NDF files), you can restore it using SQL Server Repair Toolbox by selecting all MDF and NDF files in the source file selection dialog. To select all files, press and hold the CTRL key while selecting files with your mouse. You can also press and hold the Shift key and use arrow keys to modify the selection box and select the necessary files.
Note: files with the *.ldf extension contain logs of current operations and don’t need to be selected for database repair.