Expedit shelf outer edges are hollow. You have to attach hinges in the thin partitition walls. You will nead two sizes of doors: 39cm X 79.5cm on the edges of the cabinet and 34,5cm X 79,5cm size in the middle.
Before attaching the doors drill opening holes in every door or use knobs. In my case, holes are 35mm. Holes at the bigger doors are a little farther away from the edges so that the thick edge of the structure won’t show through. Varnish your door with furniture lacquer so you will get the dirt out of them in the future.