To enter or exit the demo mode on PRS-350, do the following:
1. On the bottom edge of the Reader, using a paper clip, press the
RESET button.
3. Turn on the Reader.
3. While the screen displays Opening book... , simultaneously press and hold both the
turn page right (2nd button from the left) and the
zoom button (4th from the left) until you see the home screen.
To check if you're in the demo mode, look at the "Settings" menu item then “About”. In the Device Information section the listing for version will show the firmware version and if it is demo mode or not.
Tested on my SONY PRS-350