Hello, CAD Assistant one of our applications, that is based on OCCT library.
There is a sample to convert files. To convert from STEP to OBJ you need to tessellate a model
https://dev.opencascade.org/content/dewrapper-sample-harnessing-occt-de-...
OCCT documentation:
https://dev.opencascade.org/doc/overview/html/occt_user_guides__de_wrapp...
Repo:
https://github.com/Open-Cascade-SAS/OCCT
https://dev.opencascade.org/resources/git_repository
More information: https://dev.opencascade.org/resources
Best regards, Commenter-1.