Autodesk now primarily operates on a subscription model for its software, including AutoCAD. Subscribing to AutoCAD provides you with the latest versions, updates, and support without the need for product keys.

A product key is a unique code that is required to activate a software product. In the case of Autocad 2018, the product key is used to unlock the full range of features and functionalities of the software. Without a valid product key, users can only use the software in trial mode, which has limited features and functionalities.