Abstract: Relatively tall stacks of paper sheets are introduced into successive cartons from above while the cartons are confined in the chamber of a receptacle whose side walls prevent excessive outward bulging of the adjacent side walls of the carton when a stack descends toward the carton in a vertical duct whose cross-sectional area is just sufficient to allow the stacks to descend. Each descending stack pushes a column of air into the carton wherein the air is compressed and urges the side walls of the carton against the respective side walls of the receptacle. The upper end of the duct receives stacks from an upright container having a bottom wall which is movable between open and closed positions. A side wall of the receptacle is detachable or otherwise movable to an open position so as to allow for insertion of empty cartons into or for removal of filled cartons from the chamber.