PDF to PowerPoint

Yes. Rendering pages and building a deck needs a server, so this file is sent over an encrypted connection. The copy there is deleted as soon as the result is sent back, unless you are signed in and asked to keep it.

Keep the look if you are presenting the pages as they are — it is exact, and nothing on the slides can be edited. Make it editable if you need to change the words — the text becomes real text boxes, and some of it may shift. Keeping the look is the default because it cannot get anything wrong.

Because a PDF does not record a layout. It records where each piece of text and each image was drawn, with no note of what was a title, a bullet or a column. Rebuilding that as slide objects means reading positions back and placing them, which lands close but rarely exactly.

In Keep the look, yes — a scan converts perfectly, because the page is rendered as a picture either way. Make it editable is refused with a clear message, because a scan has no text to rebuild from. Run it through OCR PDF first if you need editable text.

The deck takes the first page's shape, and every other page is fitted inside it whole — same proportions, centred, with margins where the shapes differ. PowerPoint has one slide size for a whole deck, so a mixed document has to be handled some way; this one never crops or stretches a page.

Yes. It runs on a server rather than in your browser, so it has a cap of its own: 25 MB and 50 pages. A file over either is turned away before anything is sent.