Drop the document: each page becomes a slide, and the text is placed where it sat on the page. What comes out can be edited in PowerPoint, Impress or Keynote.
What it does not do: This is the TEXT of a PDF placed on slides, not a reproduction of the document: images, backgrounds, shapes, colours and fonts are not carried over. The text is placed at its position and size, and it will be rendered with your software's font, whose letters are not the same width: a line may therefore run a little further. Formulas and notes are not carried over. The structure is guessed from the layout: it works well on a deck exported to PDF, on a report, a manual, and badly on a free-form layout. 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.