Example:
 from pyPdf import PdfFileWriter, PdfFileReader
 output = PdfFileWriter()
 input1 = PdfFileReader(file("document1.pdf", "rb"))
 # add page 1 from input1 to output document, unchanged
 output.addPage(input1.getPage(0))
 # add page 2 from input1, but rotated clockwise 90 degrees
 output.addPage(input1.getPage(1).rotateClockwise(90))
 # add page 3 from input1, rotated the other way:
 output.addPage(input1.getPage(2).rotateCounterClockwise(90))
 # alt: output.addPage(input1.getPage(2).rotateClockwise(270))
 # add page 4 from input1, but first add a watermark from another pdf:
 page4 = input1.getPage(3)
 watermark = PdfFileReader(file("watermark.pdf", "rb"))
 page4.mergePage(watermark.getPage(0))
 # add page 5 from input1, but crop it to half size:
 page5 = input1.getPage(4)
 page5.mediaBox.upperRight = (
 page5.mediaBox.getUpperRight_x() / 2,
 page5.mediaBox.getUpperRight_y() / 2
 )
 output.addPage(page5)
 # print how many pages input1 has:
 print "document1.pdf has %s pages." % input1.getNumPages())
 # finally, write "output" to document-output.pdf
 outputStream = file("document-output.pdf", "wb")
 output.write(outputStream)