METHOD FOR PRODUCING AT LEAST ONE WINDOW OPENING IN AN ELONGATE PAPER SUBSTRATE, AND APPARATUS

The invention relates to a method and an apparatus for producing at least one window opening (7) in an elongate paper substrate (1) which is divided virtually into paper sheet sections transversely with respect to its longitudinal axis. The method comprises the following steps: a) the paper substrate (1) is provided with at least one watermark (2) per paper sheet section; b) the position of at least one watermark (2) on the paper substrate (1) is detected by means of at least one sensor unit (3); c) the paper substrate (1) is then fed to a unit for producing openings in the paper substrate (1), which unit is actuated in such a way that at least one window opening (7) per paper sheet section is produced in the paper substrate (1) on the basis of the position of the at least one watermark (2), which position is detected by the at least one sensor unit (3).