Jevrod:
After a quick test, this is what I found:
1. If you open the library part and do a Save As... and check the Save in Binary Format, the object is not saved as binary.
2. If you place the object in plan, view it in the 3D Window, then Save 3D Model As..., you will get the small dialog box where you choose the object type (Object, Door or Window) and the option to save as binary or edible GDL Script, this will save the part in binary code.
I don't know if the binary option in 1 above works in other circumstances.
David