The form supply from the upstream feeder modules takes place cyclically. Sensors constantly monitor the covering letter on the way to the following modules. They allow a complete track and trace, and they prevent any possible mismatch. The form processing exists essentially of the form reading, the labeling station for the gummed labels, the label feeding station, and the folding work. The folded or unfolded forms can either be collected together into groups, or be handed over to a letter storage box, an inserting machine file tape, or to another processing or packing system. Furthermore the forms can already be transported to a storage area before the folding work.