I frequently use the technique of copying elements of one file to a second file. This saves lots of time. However, when I first tried cutting and pasting, I had difficulty getting the second file open at the same time as the first. The trick is to open the second file not with the menu or the tool bar. The trick is to type .open This command (be sure and put the . before the open) does not close the previous drawing. The standard Open command without the . will force a close of the currently open drawing before you can open another.
Larry P
(Now that I have done it, lets have some other tips too)