Hi val2
>I looked at it in Cad Assistant???
How do you open a .3dm file in "Cad Assistant"? I've read about opening Nurbs files but I don't understand how to do it.

https://www.opencascade.com/products/cad-assistant/
Additional mesh file formats import is supported with help of Open Asset Import (COLLADA, 3DS, FBX, BLEND) and openNURBS (3DM) libraries.

Well, I think that's way beyond my capabilities. But it may be of interest to some people.
https://github.com/mcneel/opennurbs