I'm not quite sure if you want to convert your STL files to a 3D CAD format, so that your machine operator can then run it through his favourite CAM package, or whether you want to do the CAM yourself. I have used Fusion 360 to do the latter (and it's free if you are a student). Converting to a standard 3D file format is always going to be a little more difficult as it's not really a logical thing to do in most cases as straight to CAM/gcode makes more sense - but you need to know machine parameters like cutting speeds, cutter sizes, etc, to do it properly.