Your best option for handling DWG/3DS formats is to use software from Autodesk, namely 3ds Max previously also known as 3D Studio Max.
Unfortunately, direct export to 3DS format was removed in AutoCAD 2007, so this software is no longer an option for dwg to 3ds conversion. Autodesk suggests that users export their data to FBX format, which can then be used in all sorts of 3D modeling / CAD tools.
Also, some 3rd party solutions may support both .dwg and .3ds files and allow users to convert dwg to 3ds, but only certain versions of DWG format may be supported.
Updated: July 3, 2023