How to load CAD drawing with threejs，such as DWG format file
First Export cad project as fbx or obj. format
After import your file in threejs editor.
Usually, it’s not that simple in my experience. Many of the features of DWG are not in FBX, so you’ll probably need to do quite a bit of work in the CAD program to prepare the model for export, or possibly import the FBX into blender or 3DS Max and fix it there.