As an existing Papers user, you are eligible for 40% off the standard rates for the new ReadCube Papers apps. To recieve your special link, please complete this form which includes your existing Papers license key. Within 1 business day, you will recieve a custom link to complete the upgrade.
You will be asked to create a new ReadCube Papers account if you haven't already. You can use the same details as you did with Papers 3, but you won't see past purchases as it a new authentication system.