I tried to use this post to context thing but it doesn't seem to work the way I want it. I'm having trouble getting B to find the file that A posted for them. And also, when you post files like this it doesn't give you any options for which folder to put the files in.

A is in finances and has reports to send to B, C, and D. They're personal so each report can only be seen by the person its inteded for among B, C and D. B, C, and D should also be able to find all of their files aggregated in a single page so that they can quickly find them and refer to them.

Can this work with the method you're describing?