Drop the document: the structure that was found is shown before you save. What comes out is editable text, which your word processor will lay out its own way.
What it does not do: What comes out is the CONTENT of the PDF, not its layout: margins, columns, fonts, sizes, colours and page breaks are not carried over, and your word processor will lay the text out its own way. Images, formulas and footnotes are not carried over either. The structure is guessed from the layout, which is why it is shown to you: it works well on a report, a contract, a manual, and badly on a free-form layout. A page in several columns is read edge to edge, so out of order, and the screen says so. A scanned document has no text to read: run it through text recognition first.
Nothing is uploaded. Cut your network connection once this page has loaded: the tool keeps working. How to check it yourself.