This feature is available only to administrators.
Go to Documents, and from the dropdown select "Common Organization Document".
Give it a proper description, and then upload the document (PDF preferably).
This document will immediately become visible to all your employees on their dashboard. You can add more documents by repeating this procedure. If you delete any such document, then it will be removed for all employees as well. Please note that only administrators and user roles who have been specifically granted this permission are able to upload common documents.