It's not so true:
AutoCAD provides automation through
AutoLisp and/or
VBA, but this means that you
"embed" some code into
AutoCAD to extend its capabilities; for instance you can write an
AutoLisp or
VBA routine that load a drawing from your own file format.
If you have a project written with
VC6, you can add it functioalities to export drawings to
DXF files and then load them into
AutoCAD; there are plenty of
C/C++ libraries that you can find on the internet to do that.
Personally, I used
dxflib[
^] to add
DXF import/export functionalities to some software of mine.