Re: adding documents and files to a contact
It may help us to help you if we could know which hardware model and software version you are using.
Eg: On my MacBook Pro using MacOS 13.7.8
Can click on "edit" at bottom right on a contact card to add whatever details I wish under "Note" at the end.
Would likely add the links, (or a note about the location)s)) to any associated files or folders on my Mac.
(Seems unwieldy to try adding all correspondence there,
eg: a collection of correspondence in a folder of same contact name, possibly in the Documents folder,
is easy to access.)
Another way to find everything quickly is to use the contact's name in a "search" field in a Finder window,
in order to see everything related that is stored on Mac.