An electronic device with a touch-sensitive display and one or more sensors to detect signals from a stylus associated with the device: displays a user interface in a viewing mode, the user interface including a content region and a first control region; while displaying the user interface in the viewing mode, detects an input by a first contact on the touch-sensitive display; and, in response to detecting the input: when the first contact is a stylus contact in the content region: changes from the viewing mode to an editing mode; and displays, in the content region, a mark drawn in accordance with movement of the first contact; and when the first contact is a non-stylus contact in the content region: remains in the viewing mode; and performs a navigation operation in the content region in accordance with movement of the first contact without displaying the mark.