Canon MX870 Series User Manual page 552

The Password dialog box opens. Enter the password and click OK.
2.
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
In the View & Use window, select PDF files and click PDF or Print.
1.