CMX is legacy and read-only here
CMX is an older vector format. It can usually be opened and converted from, but it's long obsolete, so there's no modern encoder to create new CMX files.
Looking for DWG to CMX? Here's why CMX isn't an output option — and the modern formats to use.
We don't create CMX files — it's a legacy format that's effectively read-only. Here's what to convert to instead.
CMX is an older vector format. It can usually be opened and converted from, but it's long obsolete, so there's no modern encoder to create new CMX files.
For a file that opens everywhere, convert your DWG to SVG, PDF or EPS instead.
DWG is AutoCAD’s native format storing precise 2D/3D vector geometry for engineering and architecture.
How to open DWG opens in AutoCAD, DraftSight, LibreCAD and BricsCAD.
Full DWG format guide