On the one hand, it provides proof that the software was purchased legally from Microsoft or an authorized reseller, on the other, it provides in-depth information on the rights obtained with the purchase of a specific software program, besides the terms and conditions of the agreement through which the purchase was made.
While the agreements, the ordering documents or the invoices with all the rights they contain are in your possession and all you have to do is keep them safe, the online documentation has to be accessed and followed on a regular basis because it is subject to change. You should keep track of the changes in the online sources, to understand what you are entitled to use at a certain moment in time, in a changing world.
In this article, you will find an overview of both the offline (private) and online (public) sources relevant to ensure your Proof of Entitlement (PoE) is up-to-date. It is strongly advised to have this up to date as, in case of a conflict, it is your responsibility to be able to hand over your Proof of Entitlement.