Python code steps to add watermark to PDF

Step 1: Install the necessary libraries

First, make sure you have installedPyPDF2andreportlabLibrary. If they are not installed, you can install them via pip using the following command:

pip install PyPDF2 reportlab

Step 2: Prepare the font file

Since we want to use Chinese in watermarks, we need to prepare a Chinese-supported font file, for example (bold). Make sure that this font file is in the same directory as your Python script, or you know its full path.

Step 3: Write Python scripts

Next, we write a Python script to generate a watermark and add it to an existing PDF document.

import io
from PyPDF2 import PdfWriter, PdfReader
from  import pagesizes
from  import cm
from  import pdfmetrics
from  import TTFont
from  import canvas

# Register fonts to use Chinese in PDF(TTFont('SimHei', ''))

# Functions that generate watermark filesdef create_water_mark(text):
    packet = ()
    # Create a new PDF page as a watermark    my_canvas = (packet, pagesizes.A4)
    # Set the watermark font and size    my_canvas.setFont("SimHei", 20)
    # Set the fill color to black    my_canvas.setFillColorRGB(0, 0, 0)
    # Set transparency (0.0 is completely transparent, 1.0 is completely opaque)    my_canvas.setFillAlpha(0.1)
    # Rotate the font to increase the watermark effect    my_canvas.rotate(30)
    # Draw watermark text multiple times on the page to form a watermark pattern    for i in range(3, 24, 10):
        for j in range(-5, 30, 5):
            my_canvas.drawString(i * cm, j * cm, text)
    my_canvas.save()
    (0)
    # Return to the PdfReader object of the watermark page    return PdfReader(packet)

# Functions that add watermark to PDF filesdef add_watermark(input_pdf_path, output_pdf_path, watermark_text):
    # Create a watermark    watermark = create_water_mark(watermark_text)
    # Read input PDF file    pdf_reader = PdfReader(input_pdf_path)
    pdf_writer = PdfWriter()
    # traverse each page of the input PDF and add a watermark    for page in pdf_reader.pages:
        page.merge_page([0])
        pdf_writer.add_page(page)
    # Write a PDF with a watermark to the output file    with open(output_pdf_path, "wb") as output_pdf:
        pdf_writer.write(output_pdf)

# Main Programif __name__ == '__main__':
    # Input and output PDF file paths    input_pdf = r""  # Replace with your input PDF path    output_pdf = r"output_with_watermark.pdf"  # Expected output PDF path    watermark_text = "Add watermark test text"  # Watermark text content    # Call the function to add watermark    add_watermark(input_pdf, output_pdf, watermark_text)

Step 4: Run the script

Save the above script as a.pyDocumentation and ensureThe font file and the script are located in the same directory. Then, run the script on the command line:

python your_script_name.py

Willyour_script_name.pyReplace with the file name of the script you saved.

Step 5: Check the results

After the script is completed, check the specified output directory and you should see a name calledoutput_with_watermark.pdfnew file. Open it and you will see that the specified watermark text is added to each page.

Things to note

make sureThe font file is in the same directory as your script, or its path is correctly specified.
reportlabThe library is used to generate watermark pages, andPyPDF2Library is used to read and write PDF files and merge pages.
The transparency and rotation angle of the watermark can be adjusted as needed.
The code in this tutorial is a basic example that may need to be modified and optimized according to the situation.

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