Polygon files (.ply) are usually accepted in almost every 3D modeling software and even some CAD programs so you should be able to use for making new parts and other CAD elements that can be later exported and saved as DWG files from AutoCAD.
Convert Polygon graphics to AutoCAD drawing.
We found 3 software records in the database related to .ply to .dwg file format conversion.
Microsoft Windows software - convert ply to dwg on Windows
Leading 2D and 3D CAD development software from Autodesk
Convert from ply file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned ply to dwg. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A 3D CAD translation softwate
Apple macOS / Mac OS X software - convert ply to dwg on OS X
Mac version of popular Autodesk AutoCAD software