To register your copy, follow these steps provided by Quite Software :

Click . If successful, the watermark will disappear from all future impositions. Where to Find a Valid Serial and Private Code

Version 5.3 is particularly significant because it added "native" support for Apple's M1 and M2 chips (Silicon Macs). If you are running a modern macOS like or Sequoia , you must be on version 5.3 or higher to ensure stability within Adobe Acrobat.