I have a deathmatch map and I want to convert it to a CTF map, for that I want to do a symetric map is it possible to copy/paste all the elements of my 1st map to have a perfect symetric map?

yes its possible, just hold ALT and click all the polygons you want to copy, then press the copy button, and then the paste button.
you can move all the polygons now by dragging them while holding the SHIFT key.

thanks to you