Symptoms

When trying to activate FineReader with a serial number, the error message appears:

Invalid serial number.

Cause

Misprint in the serial number that is being used for the program activation.

Or the license corresponds to a different version of FineReader: "This serial number cannot be used for ABBYY FineReader PDF" error during activation. 

Resolution

To resolve the issue, please check the correctness of the serial number entered.