What is a PAD file?
The PAD file (Paper Application Definition) describes the layout and functionality of the paper product. It is used by the intended application (via the Pen API) to interpret the information coming from an Anoto functionality enabled pen.
PAD file includes information about the positioning of the page elements, like user areas, drawing areas, etc., on the paper. Application receiving data from a pen needs this information to be able to connect strokes to user areas and also for positioning process during rendering.