Canon PIXMA MX870 - Manual (Page 552)

2. The Password dialog box opens. Enter the password and click OK.
The PDF file opens in the Zoom in dialog box.
Note
To reopen the file after closing the Zoom in dialog box, re-enter the password.
Entering a Password (Permissions Password) to Edit or Print a File
1. In the View & Use window, select PDF files and click PDF or Print.
Page 552 of 1127 pages Opening/Editing Password-protected PDF Files