Carbonless copy paper works in a fairly simple way. It consists of sheets of paper that are coated with micro-encapsulateddye or ink and/or a reactive clay.
The back of the first sheet is coated with micro-encapsulated dye. The lowermost sheet is coated on the top surface with a clay that quickly reacts with the dye to form a permanent mark. Any intermediate sheets are coated with clay on top and dye on the bottom.
When someone writes on the sheets, the pressure from the point of the writing instrument causes the micro-capsules to break and spill their dye. Since the capsules are so small, the print obtained is very accurate.
Similarly, the paper can be used in dot-matrix and impact printers, where the striking head releases dye to interact with the clay.