Click the "File" menu and select the "Open" command from the context menu. Navigate to an AutoCAD file with a 2-D model that you want to convert to 3-D and double-click on it.

Use free software DXF2GCODE to convert an AutoCAD DXF (Drawing eXchange Format) file to CNC compatible GCode (Geometric-Code).

Basically, an STP file is used to store 3D models and to transfer 3D data between CAM and CAD software. STP file is stored in text-based ASCII format in STEP Application Protocols ISO 10303-2xx rules.