I opened the pmdb file in SpaceClaim 2019 R2 and found a faceted Surface Body.

You can save this as a STL file if you want to access the facets outside of ANSYS.  I can read that STL file back into SpaceClaim and get the same object back. The Student license has no limitation on the number of facets on STL files and faceted surface bodies. There are 17,432 facets.

Your issue is you are trying to write a facet body to a STEP file. Don't do that. Convert the facet body to a solid body, then you can save the solid geometry into a STEP file, but only if you have an Academic (unlimited) license. You can't do this with the Student license because of the 300 face geometry limit.