Your question has a very broad answer. You can find a very comprehensive list of CAD file formats by extension >here<.
The native AutoCAD file extension is .dwg but this database extension gets revised every few years. You may choose a target version of the .dwg file to save when working with AutoCAD.
The Drafix extension .dxf that is also very common with AutoCAD is a very broadly used extension for sharing AutoCAD files with other application platforms.
If you are seeking more specific information please state the question more specifically.
Hope this helps,
Blaine
Blaine Young
Senior Engineering Technician, US Army
