A Python script for adding margins to PDF files

add_margins_to_pdf.py

#!/usr/bin/env python3
#
# Adds margins to the given PDF file.
#
# Requirements:
#
#     pip install pypdf
#
# Usage:
#
#     python add_margins_to_pdf.py <input.pdf>
#
# It creates a file named `<input>-margins.pdf`.
#
# (Written with the help of Claude Sonnet 4.5.)
#

import pathlib
import sys

import pypdf

margins_cm = 1.5
margins_pt = margins_cm * 28.35

reader = pypdf.PdfReader(sys.argv[1])
writer = pypdf.PdfWriter()

# Clone the reader to preserve all the metadata and outline.
writer.clone_document_from_reader(reader)

# Modify each page except the first one, which usually contains the title
# image.
for page in writer.pages[1:]:
    # Get the original dimensions.
    original_width = float(page.mediabox.width)
    original_height = float(page.mediabox.height)

    # Create a new page with larger dimensions.
    new_width = original_width + 2 * margins_pt
    new_height = original_height + 2 * margins_pt

    # Translate the content to the center with the margins.
    page.add_transformation(pypdf.Transformation().translate(margins_pt, margins_pt))

    # Set a new mediabox.
    page.mediabox.lower_left = (0, 0)
    page.mediabox.upper_right = (new_width, new_height)

# Write the output file.
out_pdf_name = pathlib.Path(sys.argv[1]).stem + "-margins.pdf"
with open(out_pdf_name, "wb") as f:
    writer.write(f)