pdf-diff

The tool operates in two main stages:

1. Text Comparison: It compares the text layers of two PDFs. It serializes the PDFs into bounding boxes, performs a diff using fast_diff_match_patch, and identifies changed text hunks.
2. Visual Rendering: It rasterizes the changed pages into PNG images (using pdftopng), realigns page coordinates, draws red outlines around the changed text, and crops the image to remove unnecessary margins before stacking the pages into a final output.

pdf-diff requires libxml2 (>= 2.7.0), libxslt (>= 1.1.23), and poppler. Installation commands depend on your operating system.

# Ubuntu
sudo apt-get install python3-lxml poppler-utils

# OS X
brew install libxml2 libxslt poppler

You can install pdf-diff via PyPI using pip or directly from the source code using setup.py.

# From PyPI
pip install pdf-diff

# From source
sudo python3 setup.py install

To find differences between two PDF documents and generate a single large PNG image that highlights changes with red outlines, run the pdf-diff command followed by the 'before' PDF, the 'after' PDF, and redirect the output to a file.

pdf-diff before.pdf after.pdf > comparison_output.png