Watermark pdf

import pypdf

template = pypdf.PdfReader(open('superduper.pdf', 'rb'))
watermark = pypdf.PdfReader(open('water.pdf', 'rb'))
output = pypdf.PdfWriter()

for i in range(len(template.pages)):
    page = template.pages[i]
    page.merge_page(watermark.pages[0])
    output.add_page(page)
 
with open('watermaked_output.pdf', 'wb') as outputFile:
    output.write(outputFile)