a system for progressively folding a sheet as it continuously moves along a feed path from a printer to an envelope inserting station ; said system including an arrangement for initially forming longitudinal score lines on a sheet and for then progressively laterally bending and creasing the sheet along said score lines to as to form a folded sheet having a plurality of mutually overlying panels . the scoring and lateral bending operations take place in a progressive manner as the sheet continuously moves along its substantially linear feed path .