1. There's a manual for L4D (PC version)? I never even knew. I have no idea how to get the L4D2 manual, but if you have any questions, I guess you can ask them in the l4d2 forums on steampowered...
2. I'm not exactly sure, but I think it's the same as campaign except:
- No revive - you're down = you die, I don't think you respawn in a closet either
- No glows - teammates aren't outlined through walls etc.
That's all I noticed. I haven't played "realism" much so I don't know - maybe there's other differences too.