Merging of portions of different PCB Layouts

I was just wondering, whether there's any is any way by which we can merge the
portions of different pcb layouts(created using different PCB CAD Tool) and make a
new PCB layout file.

For e.g. I have 3 designs,
1st is created using CADSTAR(ZUKEN)
2nd using PADS(MENTOR GRAPHICS) and
3rd usung Allegro(CADENCE).

I wish to extract Power Supply portion from 1st Design, Processor section from the
2nd and Memory section from the 3rd design and combine them in a new Allegro layout.

Also I would like to add a portion of Gerbers available with me to this new Design.

Any ideas of carrying out this activity?