An automatic document feeder sits on top of the photocopier and allows you to load a stack of original documents to be scanned, copied or faxed automatically, one sheet at a time. This is far quicker than placing each page individually on the glass platen. Both reversing automatic document feeders (RADF) and dual-scan document feeders can scan both sides of a page automatically. A dual-scan document feeder scans both sides in a single pass.