catproduct to 3dxml conversion describes export of 3D model / CAD content between two formats commonly used in software from Dassault Systemes, most notably CATIA.
It will be extremely difficult to achieve such export with 3rd party software, considering only handful of 3rd party software products support CATIA's format. Which means that without CATIA, you have to mostly rely on commercial 3D converters or special plugins.