1. Suppose you have the latest version of PhantomPDF installed on your computer. If not, download it from here for English version or click here to download multilingual version.
2. Open PhantomPDF, click on the people icon in the top right corner of the window or click Help -- Subscribe, enter your Foxit account that you used to purchase the subscription to sign in.
Once your subscription is activated, you can go to Help > Manage to manage your authorized machines or change subscription. You can also go to Help > About Foxit PhantomPDF > License Information, to check licensing details, like renewal date and license modules.