WooCommmece Software Add-on
The WooCommerce Software Add-on gives you the ability to manage license keys and activations via your store.
Sell licenses and upgrades
Define your products as software via the edit product page, and after doing so lets you define software specific properties:
Order emails contain the key, activation email, and activations remaining. You can resend these emails using the in-built ‘send’ button in WooCommerce on the orders screen.
If you ever introduce a paid upgrade for software you can define valid upgrade keys, and an upgrade price, which your customers can make use of. They will just have to enter their license details during their purchase.