Do you want to edit two or more presentations at once?
Yes, you can open as many powerpoint files at once as your computers' memory
will allow. You can then copy and paste between them, etc. Just open the
files like you would in word.
Your question below is somewhat unclear. Do you want to use more than one
version of the powerpoint application at the same time? You don't need to
do that to open more than one file.