stp to idf conversion is most likely related to export of PCB designs/layout to a particular format used in CircuitWorks, the IDF format. The software was discontinued and absorbed into SolidWorks, so unless you find someone with the original tool, SolidWorks is most likely the only viable option. You can always try to reach out to SolidWorks community or even support for further assistance.
Updated: September 25, 2023