Microsoft Store('personal/common' email)
The Drawboard PDF license is linked with your Microsoft Account, there is no password/login feature for this app for most everyday users. This includes emails that end with @gmail @hotmail, etc.
Signing into this type of account within your Microsoft Store app will allow you to subscribe to PRO.
Microsoft Store for Business/Education(company domain email)
These are emails that have custom email domains (eg. @companyname.com @edu.schoolname.com)
For emails like these, you will not be able to download apps from the Microsoft Store like you normally would. You'd either need your IT admin to make it available from your Microsoft Store for Business(assuming your organization has one).
This limitation prevents you from having subscriptions (eg. Drawboard PDF PRO) as well as some difficultly gifting license codes to other accounts.
PRO isn't available on the Microsoft Store for Business, so if you intend to upgrade, we'd recommend creating an enterprise account with us(>15 licenses) or using a 'personal/common' email to access Drawboard PDF to obtain PRO instead.