Pay-Per-View(PPV) allows you to view content not covered by your subscriptions and you will be charged a transaction fee each time you view a document.
With your annual subscriptions you have unlimited access to content inside your subscription. With PPV, you have immediate access to content outside of your subscriptions on a document-by-document basis.
If content is not covered by your subscription, it will be identified with the "out of plan" sash as below. As soon as you click on a document that is outside of your subscription, a pop up will appear requiring you to accept the PPV charge before you can proceed to the document.