The only thing I can think of is that a user tried clicking the Edit PDF button and signed up for a free Acrobat Pro trial, but that requires a valid credit card but I can't imagine they signed up for that many trials...
The only thing I can think of is that a user tried clicking the Edit PDF button and signed up for a free Acrobat Pro trial, but that requires a valid credit card but I can't imagine they signed up for that many trials...