pyPdf

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)