Intel® Fortran Compiler 16.0 User and Reference Guide
You can specify additional Fortran free format and fixed format file extensions to be recognized as valid file extensions within the IDE. The IDE treats these additional extensions as compilable Fortran source files. You can also remove or modify existing extensions.
When you add a new extension, the IDE checks the registry to determine whether the extension is already associated with a language, tool, or file format. If there is such an association, a message informs you of this and you will not be allowed to add the extension.
To specify Fortran file extensions:
Open Tools > Options.
In the left pane, go to Intel Compilers and Tools > Visual Fortran > General.
Specify one or more Fortran File Extensions, each beginning with a period and separated by semi-colons. You can specify extensions for both Free Format and Fixed Format. Click OK.
These new settings take effect the next time you start Visual Studio*.
Use the Reset button to restore Fortran file extensions to their default settings.