Thanks for that Michael - yes I kinda suspected that.
Can you suggest some means of converting said file(s) into even a low res version that Moi could use?

If your object is less than 10 000 polys you can try
the _importObj by Max Smirnov http://moi3d.com/wiki/MaxScriptArchive
But you must convert first your "3dm" file --->OBJ!

or the native SubD / Create ;)

For decimate OBJ itself : Zbrush has a terrific one : Decimation Master

Maybe the free online OnShape can also make that! ;)
https://www.onshape.com

Hi Raven,

re:
> Can you suggest some means of converting said file(s) into even a low res version that Moi could use?

There is a process called "reverse engineering" (https://wiki.mcneel.com/rhino/reverseengineering) but it's a very difficult process using special and expensive tools to create larger spline patches over top of a dense polygon mesh.

Or also like Pilou writes above most polygon modeling programs have a poly reduction tool. I think there's a free one in MeshMixer you could try:
https://meshmixer.com/
https://www.youtube.com/watch?v=921cDYBpuL4

But in general it's kind of a square peg round hole type thing. It's usually not suitable to work with that type of polygon data in MOI.

You can export CAD models out to a polygon mesh which will dice up the model but going the other direction is difficult.

- Michael