Hi, I write about of DWG to DXF converter, I'm not a programmer, but I did several searches for a library dxf compatible with GPLv3, I found this: https://github.com/bert/libdxf is not very complete, but is released under the GPLv2 or any later version (I haven't found other). I hope it will be useful.
I'm sorry for my orrible English, Yours sincerely, Paolo
