In a high-speed sorter, single documents such as banknotes are successively withdrawn from a stack and tested according to various criteria. Banknotes which are authentic but no longer fit for circulation are fed to a cutting means a shredder and destroyed therein. The shredder, which has a simple construction and is designed for a high banknote throughput, consists of two cutter blocks including overlapping cutter discs which work into one another with little play in spaced relationship and are provided along their periphery with notches, and which slit and crosscut the banknotes. A suction plant prevents back-ups from forming, cleans and cools the cutting means.