PDF Imposition DE automates the process of 2up, 3up, 4up, 6up, 8up, 10up or 12up a pdf document, so for example with a/b 2up page 1 is on the left and page 2 is on the right, with split 2up (4 page document) page 1 is on the left and page 3 is on the right, then page 2 is on the next page left and page 4 is on the right.