Since its earliest days, Notes has provided document-level security that can be enforced through the use of Authors and Readers fields, extending the database ACL and allowing you to further refine the already granular and extensive security model.
Using Readers Fields
Readers fields are a very powerful document level security feature that enable you to further refine database access by restricting the users, groups, servers, and roles that can read a particular document. A Readers field is a special type of text field that interacts with the database ACL, further refining it. When a Readers field is placed in a document and users, groups, servers, and roles are named in it, access to that document is restricted to the named entities. ...