PyPDF2 pdf manipulating and writing example beginner working sample.

python_pdf.py

# This is a PyPDF2 example found in sample_code directory.
# I removed some parts which may cause problems for beginners.
# Also fixed code to work with python 3+.

from PyPDF2 import PdfFileWriter, PdfFileReader

output = PdfFileWriter()
input1 = PdfFileReader(open("sample.pdf", "rb"))

# print how many pages input1 has:
print("document1.pdf has %d pages." % input1.getNumPages())

# 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 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)


# finally, write "output" to document-output.pdf
outputStream = open("PyPDF2-output.pdf", "wb")
output.write(outputStream)

Thanks quickgrid for wonderful explanation. Only thing that got missed at the end is :
outputStream.close()