Batch Convert Images to PDF from Command Line

A friend asked me for a way to batch-convert images into PDFs. Instead of using online converters, here's a command-line solution using ImageMagick that works on both Mac and Linux. It converts all images in a folder to individual PDFs and optionally merges them into one file.

Prerequisites

macOS

Install ImageMagick via Homebrew:

brew install imagemagick

If you don't have Homebrew, install it first from brew.sh.

Linux (Ubuntu/Debian)

Install ImageMagick and Poppler utilities:

sudo apt-get install imagemagick
sudo apt-get install poppler-utils

The Script

This script converts all PNG images in the current directory to individual PDFs, then merges them into a single file:

for image in `ls *.png`; do convert $image `basename $image .png`.pdf; done
pdfunite *.pdf out.pdf

How It Works

Line 1: Convert images to PDFs

for image in `ls *.png`; do convert $image `basename $image .png`.pdf; done

• Lists all PNG files in the current directory
• For each image, uses ImageMagick's convert command to create a PDF
• The PDF has the same name as the image (e.g., photo.png becomes photo.pdf)

Line 2: Merge PDFs (optional)

pdfunite *.pdf out.pdf

• Uses pdfunite from poppler-utils to merge all PDFs into out.pdf
• Skip this line if you want individual PDFs instead of one merged file

Usage Examples

Convert all PNG images:

cd /path/to/your/images
for image in `ls *.png`; do convert $image `basename $image .png`.pdf; done
pdfunite *.pdf out.pdf

Convert JPG images instead:

for image in `ls *.jpg`; do convert $image `basename $image .jpg`.pdf; done
pdfunite *.pdf out.pdf

Convert without merging:

for image in `ls *.png`; do convert $image `basename $image .png`.pdf; done
# Now you have individual PDFs for each image

Additional Options

Control image quality and size:

convert -quality 90 -density 150 image.png output.pdf

• -quality 90: JPEG quality (0-100, higher = better quality)
• -density 150: DPI resolution (default is 72)

Convert multiple formats at once:

for image in *.{png,jpg,jpeg}; do convert "$image" "${image%.*}.pdf"; done

This handles PNG, JPG, and JPEG files in one pass.

Notes

File naming: The script preserves image filenames. scan001.png becomes scan001.pdf.

Order matters: If you're merging PDFs, they're combined in alphabetical order. Name your files accordingly (e.g., 01.png, 02.png, 03.png).

Large batches: For hundreds of images, this might take a few minutes. ImageMagick processes each image sequentially.

Cleanup: After merging, you may want to delete individual PDFs:

rm !(out).pdf  # Keeps only out.pdf

Alternative tools: If you prefer GUI tools, consider:

• Mac: Preview.app can combine images into PDFs
• Linux: GIMP, LibreOffice Draw
• Cross-platform: Online converters like jpg2pdf.org

View the original code on Gist.