What is the difference between a permanent license and a Document 365 subscription?

Permanent License

A permanent license is a license that does not expire. It continues to authorize access to PDF Reader Windows version indefinitely, but users with the license can only access the offline converter. 

Document 365 Subscription Plan

The Document 365 Subscription plan gives you access to all pro features and services you need across PDF Reader mobile and desktop apps. The plan includes quarterly and yearly plans. You will be charged based on the subscription period of the plan you choose, and subscriptions will renew automatically, on your renewal date, until you cancel. 

With Document 365 subscription, it gives you uninterrupted access to new versions and releases of PDF Reader all versions along with priority customer support.