simple, I made a letter, extruded it. Next you create a blendshape and move vertices until you get sort of a box form, or whatever you like. Than you have to create a box with the same measurements your letterbox has. line up their pivots and parent your letter to the box. Make your box a rigid body, throw a gravity field on it, create a plane or whatever and make it a passive rigid body.
Now because your letter is parented to a rigid body it does not have incoming connections on it's move and rotate which means you can animate it once your box has landed. But it will still follow and do everything your RB does. The last bounce and the blendshape transformation you than have to animate yourself.
Actually sounds complicated, but doing it is quite simple, and quick.