How to convert 3D object files to DWG format. Exporting OBJ files to DWG. Available obj to dwg converters.
It looks like that obj to dwg conversion is in most cases related to a 3D to 2D conversion, something like export of a slice or 2D view from a 3D model (.obj) to DWG graphics. It is likely that this can be done using lots of different 3D modeling tools or even some dedicated converters.