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.

Are you trying to it, activate it, or looking for alternatives ?

Due to the security risks, the best course of action is to move to a supported version (Acrobat DC) or use alternatives like Foxit or PDF Xchange.

Because it hasn't been patched since 2017, using XI Pro is highly insecure.

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