Hi,

I would start with custom module documentation. It shows you have to make the section available only for appropriate roles and how to make the content available only for particular roles:
Developing custom modules

Then to find appropriate documents you can use smart search API:
Smart search API
For example take a look at SearchText() method.

Now to display results you need to write a transformation. You can find inspiration on a Corporate site (in some smart search web part) or take a look atsearch results transformation

In the smart search result will be available nodeID or documentID and this way you can use document API to update document:
Managing documents

Best regards,
Ivana Tomanickova