You get a unique code in the box that allows you to download the software installer via the internet but it is not a subscription. Boxed editions are “medialess” and do not contain installation media/discs. NOTE: You can buy Office 2019 as perpetual licensed / boxed editions but you won’t get proper access to the Office apps for mobile devices including iOS (iPad/iPhone).
The easiest option is to upgrade to Office 2019 but do be aware of the following before upgrading: