I was able to do this same thing. I used the Edit Area/Edit All Floors. I then put a box around what I wanted to copy. I then chose Edit/Copy. I went to the target and I chose paste/hold position (since I wanted it to be placed in the same location in the target drawing). I did have to redo the stairs because it broke them, but everything else seemed to work. Also, just so you know, you can have both files open at the same time ...