How to Combine Multiple Images into One PDF Using Python (Step-by-Step Tutorial)

[Rajeev Bagra]

In many programming projects—especially in courses like MIT’s introductory CS programs—you are often required to submit multiple images as a single PDF file. Instead of using online tools, you can do this professionally using Python and the Pillow library.

In this tutorial, you will learn how to:

✅ Open multiple images in Python
✅ Convert them to PDF-compatible format
✅ Combine them into a multi-page PDF
✅ Understand how append_images works

No prior experience with PDF generation is required.

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🧩 Step 1: Install Pillow (If Not Already Installed)

Pillow is the modern image-processing library for Python.

Install it using:

pip install pillow

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🧩 Step 2: Import the Image Module

Start by importing Image from Pillow:

from PIL import Image

This module allows you to open, edit, and save images.

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🧩 Step 3: Open and Convert Images to RGB

PDF files require images to be in RGB mode.
So we first open each image and convert it.

images = [
    Image.open("image1.png").convert("RGB"),
    Image.open("image2.bmp").convert("RGB"),
    Image.open("image3.jpg").convert("RGB")
]

Why .convert("RGB")?

Some images may be:

• grayscale ("L")
• palette-based ("P")

These formats may cause errors when saving as PDF.
Converting to "RGB" ensures compatibility.

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🧩 Step 4: Save Images as a Multi-Page PDF

Now we use Pillow’s .save() method:

images[0].save(
    "output.pdf",
    save_all=True,
    append_images=images[1:]
)

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🧠 Understanding This Code

Let’s break it down:

images[0].save(...)

Uses the first image as the first page of the PDF.

"output.pdf"

Name of the PDF file to be created.

save_all=True

Tells Pillow that multiple pages will be saved.

append_images=images[1:]

Adds the remaining images as extra pages.

images[1:] means “all images except the first one.”

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🧩 Step 5: Run the Script

Save your file as make_pdf.py and run:

python make_pdf.py

You will get:

output.pdf

containing all your images in order.

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✅ Example: MIT Assignment Submission

If your files are:

filtered_image_15_kerb.png
hidden1_unhidden_kerb.bmp
hidden2_unhidden_kerb.bmp

Use:

from PIL import Image

images = [
    Image.open("filtered_image_15_kerb.png").convert("RGB"),
    Image.open("hidden1_unhidden_kerb.bmp").convert("RGB"),
    Image.open("hidden2_unhidden_kerb.bmp").convert("RGB")
]

images[0].save(
    "submission.pdf",
    save_all=True,
    append_images=images[1:]
)

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🛠 Optional: Resize Images Before Combining

If images are too large, resize them first:

images = [img.resize((800, 1000)) for img in images]

Do this before saving.

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⚠️ Common Errors and Fixes

❌ Error: “cannot save mode L as PDF”

✅ Fix: Add .convert("RGB")

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❌ Only one page in PDF

✅ Fix: Add save_all=True and append_images

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❌ FileNotFoundError

✅ Fix: Check file names and folder location

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🌍 Real-World Uses

This technique is useful in:

• college assignments
• project documentation
• scanning workflows
• reports and portfolios
• automation systems

Many companies automate report generation using this method.

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📌 Final Takeaway

Using Python and Pillow, you can easily convert multiple images into a professional, multi-page PDF using just a few lines of code—no online tools required.

 

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