Tip for you if you're going to import poser documents (or merge as you say):

If you have a set saved for example a room and you have lights in the room and you import another Poser scene you will also import the lights meaning that you will end up with the lights from both scenes (very bright). If you want to keep the lighting from your room then save the lighting, import the scene and then apply your lighting.

That way you will end up with all the elements from both scenes but only the lighting you want.