Activation servers for older products have been shut down, often causing perpetual licenses to revert to a "30-day trial" or show "invalid serial number" errors.

It is not officially supported on Windows 11 or recent macOS versions (like Catalina and later), though some users have had success running it in compatibility mode. Solutions and Workarounds

To reinstall, users have had to contact Adobe directly for a valid download link, as public downloads were removed.

Note: You may still find perpetual, physical copies for sale on secondary markets like eBay . To provide the best advice, could you tell me:

If you have a valid license and it is stuck in a 30-day trial, you may need to contact Adobe Support or try the Microsoft Compatibility Administrator to disable pdapp.exe .

Knowing this will help me provide the exact solution you need. ACROBAT XI PRO SHUTTING DOWN - Adobe Community