When you try to open PDF OCR X, you see a message saying "You can't use this version of the application PDF OCR X with this version of Mac OS X.". You may receive this message if your Mac is running an older version of OS X that is not supported by PDF OCR X. PDF OCR X 2.0 requires Mac OS X 10.6.8 (Lion) or higher. If you are running an older operating system (e.g. Leopard (10.5), you can still use PDF OCR X 1.9.36 which is available for download on the downloads page of the PDF OCR X website.