Can someone tell me how to import attached STP / STL file as a solid body object?

Using 2019 SWX, I've been unsuccessful getting a solidbody part file. Am getting surface only. Don't know how to make modifications to it. Files are attached here.
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sorry but valve-cap.stp is a volume model our should be one, greets leo
what i have seen zour step is a not standard conform step model.
btw, why is this path in java notation and what software did create the model, to help zou further?
i have an idea, please let me now the details.
FILE_NAME('C:\\Users\\SCW_User\\AppData\\Local\\Temp\\Alibre Design\\export-CDD5FF05-7B2E-441A-94F2-6F64873890C2.stp',
greets leo