Link documents

I was wondering, is there any way to link documents?
For example, I have some letters from my bank when I opened some accounts, with it came the terms and conditions.
Instead of saving the T&S several times, I want to have it as a separate document and just link it to the two letters.

To make it mor complicated I opened another account later and with it came a revised T&S, that is only applicable to the last account, but if I later opened another account for my wife, it would have the same new T&S.

Sure. Just have a look at the “(Insert) Link To” submenu of the contextual menu of rich texts or the command Edit > Copy Item Link.