What “processed in your browser” means

A PDF is read by a library running in the page. An image is drawn on a canvas. A password is chosen with the Web Crypto API. The result is downloaded from the tab. There is no account and no upload step for the file.

What still leaves the device

Opening the website requests the page, the same way any site does. That request does not include the file you later drop on a tool. Finishing a tool can send the tool name and a random id so use can be counted. Background Remover downloads a model the first time. PDF text recognition loads an English language file from this site. None of those requests includes the file you are working on.

What you should still avoid

• Do not paste passwords or customer data into a shared or recorded screen.
• Closing the tab discards the file from the page. It does not delete a copy you already downloaded.
• Browser extensions can read a page. A private tool cannot disable an extension you installed.

The privacy page states the same boundary in full, including how to clear what this browser kept.