what is the most common type of CAD files that cnc machines can accept?

.dxf files are the most common accepted cad format for CNC machines, preferably in polyline format

Every CNC setup is different and you should take notes about your set up.
Keep a log of the different file types and what works with your setup.
This will become apparent soon enough.
Examples of Different File Types .ai - Adobe Illustrator Artwork (AI) is a proprietary file format developed by Adobe Systems for representing single-page vector-based drawings in either the EPS or PDF formats.
The .ai filename extension is used by Adobe Illustrator.
.eps - Encapsulated PostScript, or EPS, is a DSC-conforming PostScript document with additional restrictions intended to make EPS files usable as a graphics file format.
.hpgl - HPGL, sometimes hyphenated as HP-GL, is the primary printer control language used by Hewlett-Packard plotters.
The name is a set of initials for Hewlett-Packard Graphics Language.
It later became a standard for almost all plotters.
.dxf - AutoCAD DXF (Drawing Interchange Format, or Drawing Exchange Format) is a CAD data file format, developed by Autodesk as their solution for enabling data between AutoCAD and other programs.
.dwg - DWG ("drawing") is a format used for storing two and three dimensional design data and BIM metadata, it is the internal format for the AutoCAD Computer Aided Design package.
.3dm - The main file format of Rhino3D is called 3dm.
It is very useful especially for the exchange of NURBS geometry because it is released as an Open Source Toolkit called openNURBS, which is provided by the developers of Rhino3D.

.dxf - AutoCAD DXF

Cnc machines run from Gcode via a Gcode interpreter ! The Gcode is created from Cad type files by means of Cam software! The most comon file is Dxf

.dxf for the2D files and .STL for the3D files

To run a CNC machine you need a G-code file.
You can write this file manually or you can use CAM software to generate the G-code file for you.
In CAM software you can model your part and then machine it, or you can import your part from CAD software.
Nowadays CAM software accept most CAD format.

.CATPart : Its pretty expensive software usually used for the aerospace/transportation industries.
.ipt (parts), .iam (assemblies) and .idw (drawings).
.dxf : Drawing Exchange Format and Thanks

NC & G-CODE are the most common formats which is comand in machine languange which consist on the G (for coordination commands) and M (control & safety command) .

after the cad procedure you have to take that (dxf or dwg ) to post processor (cam ) where toolpath (tools ,machine limits ,home position ,movement direction assignment in + or -)have been assigned already .so the cam creat machine movement ,asigned tool change and profile processing sequences thats all.

CAD CAM PROGRAM