Users that have access to SolidWorks can simply import STEP product data (.stp, .step) to it and save as part file (.prt, .sldprt), which is pretty much what stp to prt conversion is. Except for that, some 3rd party CAD conversion programs like the CrossManager or similar can also help you to convert stp to prt.
Open STP file Open PRT fileA CAD converter with huge format support