OK, a quick "how to" on removing the rear door cards on a W124
1, wind the window fully down - this makes putting everything back together a lot easier
2, remove the ashtray and unclip it's surround (not entirely neccessary but it makes life easier and it's one less thing to risk damaging)
3, as Spike says remove the trim around the door handle and undo the bolt that's behind it. Disconnect the window switch at the same time
4, remove the surround from the door lock mechanism.
5, get your fingertips under the bottom edge of the door and lift. It may need quite a firm lift to release it but as long as you are lifting upwards there is nothing to damage.
That should free the door card for you.
Reassembly is the reverse procedure but is better done with two people, one to press the door panel against the door and to guide the lower clips on (particularly the one behind the door handle) and the second person to press downwards and guide the top clips in.
HTH
Andy