Bluebeam Software got patent #7,971,149 for the document comparison feature in its PDF Revu software. It does the following:
- Automatically scales, rotates, and aligns the selected base and revised drawings.
- Highlights differences with cloud annotations on a copy of the modified PDF.
- PDFs are synchronized; as you pan or zoom one, the other follows.
- Batch compare multiple revision sets.
- Select portions of drawings to compare.