If the database you use to store index information has security access features, you can use these to manage access to documents with SimpleIndex retrieval mode.
In your database, create user accounts and groups and assign them the appropriate permissions to records in your document database.
In SimpleIndex, check the “Require Logon” option on the Logging tab to force the user to logon to the database using the accounts you created. When they search and view documents, they will only be able to access records that the corresponding database user has been assigned access to.