Except for the obvious choice here - CATIA from Dassault Systemes from which CATPRODUCT files originates, it should also be possible to achieve the catproduct to step conversion with the use of several other dedicated CAD conversion programs like CrossManager or similar.
Open CATPRODUCT file Open STEP fileA CAD viewer program with conversion capabilities
A set of 3D modeling tools
A CAD converter with huge format support
A CAD visualizaton, analyzation and translating system
A dedicated CAD converter