Use SpaceClaim to open the STL file. It will be a facet body and there are no limits on how many facets. If you are on a full license (not the Student license) you can convert the STL to a Solid by simply RMB on the facet body and a menu pops up. The problem for the Student license is that each facet becomes a face and there is a 300 face limit on the Student license.
You are navigating away from the AIS Discovery experience