watermarker script to overlay a pdf onto another pdf with python

watermarker.py

# from an article by Mike Driscoll:
# http://www.blog.pythonlibrary.org/2018/06/06/creating-and-manipulating-pdfs-with-pdfrw/
from pdfrw import PdfReader, PdfWriter, PageMerge

def watermarker(path, watermark, output):
    base_pdf = PdfReader(path)
    watermark_pdf = PdfReader(watermark)
    mark = watermark_pdf.pages[0]

    for page in range(len(base_pdf.pages)):
        merger = PageMerge(base_pdf.pages[page])
        merger.add(mark).render()

    writer = PdfWriter()
    writer.write(output, base_pdf)

if __name__ == '__main__':
    watermarker('uc491-a.pdf',
                'uc491-b.pdf',
                'uc491b-on-top-uc491a.pdf')