A conductive path that has been printed onto a surface can be modified to serve as a touch-sensor by connecting it to a micro controller board or Microcontroller (e.g. an Arduino Uno Board or Attiny85 microcontroller). For more details: Arduino Playgroud Tutorial.
Due to a change of the measured capacity when there is a nearby finger or another human body part will be detected and this changing can be an used to trigger a programmed operations. In my explorations I mainly used a LED or an acoustic signal as an exemplary output for a detected touch.
Creating different touch-sensitive areas, the paper can be devided in several touch-sensitive areas. Thus allowing to rapidly build a keyboard-like input.
Video with sound: