A double-sided feeder runs the empty backs of a single-sided bundle. The tool measures them, ticks them, and shows you which ones before removing anything.
What it does not do: It is an ink measurement, so it is a guess: a very faint pencil note can pass for empty, and a page smudged by the scanner for full. That is why the tool shows and ticks instead of removing on its own. It does not read the content: a page carrying only a white image is empty to it as to the eye. The pages are redrawn: clickable links, bookmarks, form fields and accessibility tags do not survive. And what falls outside the frame stays in the file without being shown, as with cropping: an editor can bring it back.
Nothing is uploaded. Cut your network connection once this page has loaded: the tool keeps working. How to check it yourself.