This add-on uses the rhino3dm.py
module
(https://github.com/mcneel/rhino3dm) to read in 3dm files.
Tested with Blender 4.1.
On Windows and MacOS you need to create a zip file with the folder import_3dm.
- Create ZIP archive
- Open Blender preferences
- Open Add-ons section
- Click Install... button
- Select the downloaded ZIP archive
- Click Install
- Enable the add-on
- Probably restart Blender