Highlight textual and visual differences between two PDF files.
When a programmer compares two source code files, the computer simply runs a string comparison algorithm (like Myers Diff) on the text. PDFs, however, are complex visual layout documents.
If a lawyer changes the font size of a contract by 1pt, the actual text strings inside the file remain identical, but the visual layout has shifted. A simple text diff would miss this entirely.
The most reliable way to compare two PDFs is to rasterize them into images and mathematically compare the exact pixel values at every coordinate.
This tool uses a Pixel Matching algorithm (similar to pixelmatch) that analyzes the RGB values of both documents. When it detects a mismatch between Pixel A and Pixel B, it paints that coordinate bright red, ensuring no sneaky visual changes slip by.
Comparing high-resolution images pixel-by-pixel requires looping over millions of data points per page.
If we ran this loop on the main browser thread, the entire webpage would freeze. By running this intensive pixel matching algorithm in a background Web Worker, we keep the UI thread unblocked even when you are comparing dozens of pages.
Why is a visual pixel diff more secure than a text diff for legal documents?
