ok thank you, ichsano.ronaldo so what is the difference among those two words?

i will try to explain: "related document" means like a.. i will give you example, this is a short conversation : A : bring me some of fruit's related documents B : ok, here is the banana documents, apple documents etc.. so related document means the documents that are related to (something)..

What about the related document and the relating document? Which one is correct? Could you please explain?

"Related to" is passive and "relating to" is active. It's better giving us the completed sentace.