3D models and data saved in STEP product files (.stp, .step) are usually well-supported in modern CAD / 3D modeling tools so you should have no problem with its import. You will just need to use software that supports formats from CATIA, that is if you do not have access to CATIA itself. Some viable alternatives are listed below.
Convert ISO-10303 STEP product data to CATIA V4 model file.
We found 3 software records in the database related to .step to .model file format conversion.
Microsoft Windows software - convert step to model on Windows
A PLM/CAD/CAM/CAE software suite
Convert from step file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned step to model. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A feature rich 3D CAD software by Siemens
A CAD visualizaton, analyzation and translating system