PDFnUP software automates the process of 2up'ing, 4up'ing or 6up'ing a PDF document, so for example with a/b 2up page one is on the left and page two is on the right, with split 2up (4 page document) page one is on the left and page three is on the right, then page two is on the next page left and page four is on the right. It has an optional -down parameter for 2up'ing downwards on a page rather than across the page (left, right) The output page size can also be controlled and the second page position can be offset with margin controls. Optional duplex options for outer-in for booklets, so for e.g. 2up 8 pages source you get output pages: 8, 1 2, 7 6, 3 4, 5 - 4 pages output for duplex printing. 4, 1 2, 3 and 1, 4 2, 3 duplex options also.