What do you mean locally? Are you asking if it’s possible to create a .3DM from an imported STEP file? Of course, if you’ve got a rhino license then you can do this easily with the Rhino application or even script this using Grasshopper. Alternatively, you can use the Rhino3dm library. Using this library, you should be able to read/write your own Rhino files. Here’s a thread which might help in getting started.