You would have to export it to FBX first. Note that with the multiple format changes (originating software => Navisworks, Navisworks => FBX, FBX => STL) you'll be losing a *lot* of precision. It's not a suitable substitute for having the original files, which is somewhat the point of providing the NWD file - it's data rich and can be viewed in-context with other content, with less risk of the model being used where it shouldn't.
If this is being used as a reference, I would suggest referencing the NWD file directly in AutoCAD. I don't think Inventor has that capability yet.
----------------------------------
If you are going to fly by the seat of your pants, expect friction burns.
"I don't know" is the beginning of knowledge, not the end.
If you are going to fly by the seat of your pants, expect friction burns.
"I don't know" is the beginning of knowledge, not the end.
Both AutoCAD and Inventor can read FBX files and export as STL.
----------------------------------
If you are going to fly by the seat of your pants, expect friction burns.
"I don't know" is the beginning of knowledge, not the end.
If you are going to fly by the seat of your pants, expect friction burns.
"I don't know" is the beginning of knowledge, not the end.