A document feeder for multifunction printers or scanners offers high reliability and speedy paper-picking, -separating and -feeding functions. It comprises a picking module, a separating module and a feeding module. Since the three modules take turns to deliver paper, the paper can be picked at a lower speed, separated at a medium speed and then fed at a high speed. In addition, the separating module comprises a clutch. When the paper was fed by the feeding module, the clutch is activated to provide an interval between papers and to prevent papers from plucking.