Your selected file stays in the browser for On-device tools.
Here is the processing path in plain language.
The browser gives the page access only to the file you explicitly select.
The tool reads the selected data locally using browser APIs.
JavaScript, Web Workers or browser capabilities perform the transformation.
The browser creates the output for preview, copy or download.
What can still use the network?
The site itself must load HTML, CSS, JavaScript and other application assets. If optional analytics or advertising are introduced later, those services may also make network requests after applicable consent. That is different from uploading the selected file for processing.
What happens when I leave?
Active file references and generated object URLs are temporary. Refreshing or closing the tab normally releases the browser session. Local preferences such as theme and consent choice may remain.