EDrawings is capable of markup and saving as STL files IF the person who created the STL had EDrawings save their file with the option to save-as STL turned on.
That is in there for a couple of reasons:
1) you just want to show someone what your design looks like but you don't want them to steal it from you. In this case you disable measurement and 'save-as' (not sure what they call it exactly) STL.
or
2) you send your file to a trusted supplier that does not have Solid Works so you have measurements enabled and you also enable the save-as STL option so they can use the 3D data if needed.
Option 1 - smaller files so easier to email. Option 2 - as large as the STL file alone would be or slightly larger.
So, you might want to see if you can get the file you have issues with sent to you with the ability turned on for the receiver of the EASM file to save-as STL.
Ciao.
mshideler