You can import files into NX by using File => import => step, iges, parasolid, part etc…
But sometimes the import function seems empty. This is the result of the no part active in NX. You should create a new part or open existed part to import stp or iges files.
Another solution is opening stp/iges file by using “Open”. (File => Open) Change “Files of Type” as iges, stp or “All Files”.
You can change options for opening files by clicking the options box in the “Open” window. Options changes due to your file type selected. (stp, iges, parasolid)
For detailed import files descriptions:
