fbx to b3d conversion represents export of models between Autodesk Kaydara 3D files (.fbx) and BodyPaint 3D format (.b3d), which is most likely doable. We have not found any particular mentions of such export, but FBX is standard exchange format supported in numerous software, so the real deal will be just to find a tool that cab export/safe to BodyPaint 3D format.
Updated: April 17, 2023