Apparatus and method for trimming signatures (S) moving in a continuous stream and in an arcuate path as controlled by a conveyor (11). A trimming knife (14) is stationarily disposed adjacent the arcuate path for engaging the marginal edges (68, 68) of the signatures and trimming those edges. Input and output conveyors (10, 12) are in signature-flow communication with the conveyor (11) of the arcuate path, and either input or output conveyor (10, 12) can be reversed for the input and output function, and also the conveyor (11) having the arcuate path can accordingly be reversed so that the signatures (S) can move in either continuous arcuate path of movement for the trimming process.