Programs enabling conversion of the file:
If your objective is to convert the file from NEF to the file RAW, you can use any of the applications listed. NEF to RAW conversion process in every program intended for this purpose (so-called converters) is very intuitive and everyone is able to manage converting a file.
However, bear in mind that the list may also include programs to support and work with the indicated extensions NEF and RAW - and not only converters. In such a case, you need to open the source file NEF and from the options available in the program, choose ”Save as... RAW" or "Export to RAW".