Dear Aleksander, what do you mean with "registration"?
The order number is a string like GEA124341-1245-xxx.
To register your application and get the activation key you should:
- connect to www.androidpdf.mobi/shop/key-request
- write the order number and numeric pin you've received via email after the purchase
- press the "Order status" button
In the form you will get:
- write the application package name, the pin again
- submit the form
- validate it
- get back your key