Every privacy claim is a promise, and a promise is only as good as the check you can run on it. Two checks take under two minutes and apply to any browser tool that claims to process files locally.
Watch the network panel
Open the developer tools, switch to the Network tab, and run a full job — load a file, preview it, run it, save the result. Watch every request. A tool that keeps files on the device makes no request that carries your data: no upload, no per-file API call, no analytics ping with a filename in it. A tool that is quietly uploading is visible in that panel as a request with your file’s bytes in its payload.
Be precise about what you are looking for. A site may still send small, harmless pings — a page view, a completion event, a checkout open. What it must never send is the file, its name, or a page count.
Turn off the network
Disconnect completely — Wi-Fi off, or network settings to airplane mode — and run the whole job again. If the tool works offline, there is no server side to its processing, by construction. This is the strongest check there is, because a tool cannot quietly upload to a server that is unreachable.
If it still works offline, the claim is not marketing. It is architecture.
Not legal advice. Whether a numbering scheme or a production practice satisfies your court, protective order, or production agreement is yours to confirm.