A handheld display device for interacting with printed content. The device includes: an optical sensor for imaging an area of a printed substrate containing the printed content and generating image data; an opaque touch-sensitive display screen for displaying display output to a user; a processor configured for: monitoring the identity of the substrate and the position of the device relative to the substrate using the image data; retrieving display data; rendering the display output to the display screen; and interpreting user input captured via the display screen. The opaque touch-sensitive display screen has real-time virtual transparency through the screen to the printed content from a user's perspective to provide a virtual window to the printed content.