Local processing creates a technical boundary
A normal online converter sends bytes to a server and later returns a result. A local browser tool instead receives a File object from the file picker and gives those bytes to code already running in the tab. The output is assembled as a Blob and downloaded directly.
This removes server storage from the processing path. It does not eliminate every web privacy question: the page host still serves static assets, and optional analytics or advertisements would need separate disclosure.
Verify instead of trusting a slogan
Open developer tools and the Network panel, then process a non-sensitive test file. Network activity should consist of static site assets, not a request containing the file. You can also disconnect after the page and required modules have loaded, although first-time PDF processing needs the locally hosted PDF bundle to finish loading.
Device responsibility remains
Local processing shifts CPU and memory use to the device. Keep the browser updated, avoid untrusted documents and protect downloaded results. Closing the tab releases temporary references, but files already downloaded remain wherever the browser saved them.