Abstract: A printing apparatus has an array of cartridges for printing a web of e.g. paper passing through the array, and one or more units containing printing medium. The cartridges each are capable of transferring the printing medium from the unit(s) to the web. The unit(s) and the cartridges of the array are relatively movable, to allow the unit(s) to interact successively with at least two of the cartridges. In this way it is possible to change printing from one cartridge to another, allowing changes to be made to what is printed, without halting the movement of web significantly. The present invention also proposes that the cartridges may have printing cylinders of different sizes, and furthermore that a mobile unwind stand may be used to move web material to the printing apparatus, and the web output from the printing apparatus processed by sheet folding techniques.