You can definitely import 3D models saved in ISO STEP product data files (.stp, .step) to CATIA software and use it for making new parts (.catpart). If you do not have access to CATIA, you have to rely on some 3rd party alternatives or dedicated conversion solutions.
Convert ISO-10303 STEP product data to CATIA part data.
We found 2 software records in the database related to .step to .catpart file format conversion.
Microsoft Windows software - convert step to catpart 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 catpart. 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 CAD visualizaton, analyzation and translating system