An issue was discovered in certain Apple products. Pages before 6.1, Numbers before 4.1, and Keynote before 7.1 on macOS and Pages before 3.1, Numbers before 3.1, and Keynote before 3.1 on iOS are affected. The issue involves the "Export" component. It allows users to bypass iWork PDF password protection by leveraging use of 40-bit RC4.
https://support.apple.com/HT207595
http://www.securitytracker.com/id/1038136
http://www.securitytracker.com/id/1038135