Determine your remote desktop session ID

Create and run a batch file
tscon <session ID> /dest:console
start "" "<Netfabb install directory>\SIM\appbase.exe" "<STL file path>" ""
An example is as follows:
tscon 1 /dest:console
start "" "C:\Program Files\Autodesk\Netfabb Ultimate 2018.3\SIM\appbase.exe" "c:\test\1.stl" ""