pdf-diff

Finds differences between two PDF documents:

1. Compares the text layers of two PDF documents and outputs the bounding boxes of changed text.
2. Rasterizes the changed pages in the PDFs to a PNG and draws red outlines around changed text.

Unfortunately while I started this project in node.js, I couldn't figure out how to quickly do the rendering part in node.js and so I switched to Python where I had some similar code laying around already.

Installation

# for the comparison tool

npm install

git clone https://github.com/mozilla/pdf.js
cd pdf.js
node make singlefile
cd ..

## for the renderer

sudo pip3 install pillow

Running

# Compute the changes.

# Unfortunately the pdf.js prints warnings on STDOUT, so we have
# to filter those out.

node index.js before.pdf after.pdf | grep -v "^Warning:" > changes.json

# Render the changes.

python3 render.py < changes.json > test.png