I imported a STL with two Bodies and try to do an Edge-Blend or Face-Blend but cannot do this. The edge and faces are not selectable. Does someone know if this is possible and, if yes, what I need to do?
The reason you cannot select faces or edges is because STL bodies are faceted bodies and do not have actual faces or edges - so you're using the wrong types of modeling tools.
I'm sure someone else with more experience/knowledge about faceted/Convergent modeling might chime in, but in the meantime I'd suggest reading the Help Docs for what you can and cannot do with faceted and Convergent models in NX.