Navigate over to the products page and view the table of products.
Find the product you wish to enable or disable manuals for, and hit the 'Manage' button at end of the desired product row.
This will load you into a 'Manuals' page. From here you can click the status button located near the end of each manual file row. Once clicked, the table and status will update. Simply click it again to revert the change.
It should be finally green "Active" if you want to enable or red "Not Active" if you want to disable. 
Please note, only manuals that are active will show in the manuals list widget and product button.
