Verifying "without uploading" isn't just a slogan
Open DevTools' Network tab before running the compression — you'll see the WebAssembly binary and Web Worker script load once (and get cached for next time), but no request carrying your PDF's actual bytes. That's the practical difference between a tool that says "private" in its marketing and one where the architecture makes upload structurally impossible.
This matters most for compressing files you wouldn't want sitting on a stranger's server even briefly — scanned IDs, signed contracts, medical forms — where "we delete it after an hour" isn't a reassuring answer.