It is possible to add documents to an employee's profile and restrict its access. There are two ways to go about it: by attaching a file through file notes or by adding an attachment directly in the employee's profile (under documents).
File Notes
You can add notes in an employee's profile (file notes tab). For each note you can attach a file. This tab is never available to the employee himself. There are no access to give or remove. It is hidden by default. This eliminates the risk of giving the employee access to their files by accident.
Limit the access to files by going through the employee's profile
When adding files to the employee's profile (documents tab), you have the option to make the file available to the employee of not. If you do not wish for the employee to view the files, simply make sure that the shared to employee toggle is off. For more information about document management for employees click here.
Only individuals who have been granted access to view files in another employee's profile will be able to access them. This permission is given in the user management page.