Python Watermarker

import os
import PyPDF2
from reportlab.pdfgen import canvas
from reportlab.lib.utils import ImageReader
import io

# Step 1 - define what it means to add a watermark to an input-doc and to save it to an output-doc
# This does not require any changes, except where indicated below

def add_watermark(input_pdf, output_pdf, watermark_png):
    with open(input_pdf, 'rb') as pdf_file:
        pdf_reader = PyPDF2.PdfReader(pdf_file)
        pdf_writer = PyPDF2.PdfWriter()

        watermark_pdf = canvas.Canvas(io.BytesIO())

        watermark_pdf.setFillAlpha(0.5)
        # the number we input into setFillAlpha determines the transparency of the image
        # 0.0 - fully transparent
        # 1.0 - fully opaque
        # my default setting is
        # watermark_pdf.setFillAlpha(0.5)

        watermark_pdf.drawImage(ImageReader(watermark_png), 100, 200, width=400, height=400)
        # the numbers here determine the position and size of the watermark, you can play around with these
        # my default setting is
        # watermark_pdf.drawImage(ImageReader(watermark_png), 100, 200, width=400, height=400)

        watermark_pdf.save()

        watermark_page = PyPDF2.PdfReader(io.BytesIO(watermark_pdf.getpdfdata())).pages[0]

        for page_num in range(len(pdf_reader.pages)):
            page = pdf_reader.pages[page_num]
            page.merge_page(watermark_page)
            pdf_writer.add_page(page)

        with open(output_pdf, 'wb') as output_file:
            pdf_writer.write(output_file)

# Step 2 - We must define the paths where the program is supposed to work
# You NEED to edit the value for these 3 variables

input_folder = r'C:\Users\Anwender\Downloads\Gavel\Input'
# you NEED to edit this
# the value be of the format r'[the address of your folder for documents you want watermarked]'
# Example:
# [the address of your folder for documents you want watermarked] = C:\Users\Anwender\Downloads\Gavel\Input
# then
# input_folder = r'C:\Users\Anwender\Downloads\Gavel\Input'

output_folder = r'C:\Users\Anwender\Downloads\Gavel\Output'
# you NEED to edit this
# the value should be of the format r'[the address of your folder for the documents once the watermark has been added]'
# Example:
# [the address of your folder for the documents once the watermark has been added] = C:\Users\Anwender\Downloads\Gavel\Output
# then
# output_folder = r'C:\Users\Anwender\Downloads\Gavel\Output'

watermark_png_path = r'C:\Users\Anwender\Downloads\Gavel\Watermark_Gavel.png'
# you NEED to edit this
# the value should be of the format r'[the address of your file that contains the watermark image]'
# Example:
# [the address of your file that contains the watermark image] = C:\Users\Anwender\Downloads\Gavel\Watermark_Gavel.png
# then
# watermark_png_path = r'C:\Users\Anwender\Downloads\Gavel\Watermark_Gavel.png'

# Step 3 - Loop through all PDF files in the input folder
# You don't need to do anything here

for filename in os.listdir(input_folder):
  if filename.endswith(".pdf"):
    # Extract filename without extension
    file_name, _ = os.path.splitext(filename)

    # Construct input and output paths
    input_pdf_path = os.path.join(input_folder, filename)
    output_pdf_path = os.path.join(output_folder, f"{file_name}_WM.pdf")

    # Add watermark to the current file
    add_watermark(input_pdf_path, output_pdf_path, watermark_png_path)
    print(f"Watermarked: {filename} -> {file_name}_WM.pdf")