Stamp page numbers in the corner of every page, starting from the number you choose, so a printed document can be referenced and reassembled in order.
Numbering matters the moment a document is printed, filed or discussed: a contract refers to "page 4 of 12", a court bundle must be paginated, a manuscript gets read chapter by chapter. Adding numbers into the file itself — rather than relying on the reader's viewer — means the numbers appear on paper too.
A chapter that begins after a cover page or continues from a previous volume should not restart at 1. Set the starting number and the pages are counted from there, so the printed number matches the position in the whole work.
Put the number where a reader looks for it: bottom centre on a report, bottom right on a filing. Avoid placing it over a busy scan — on documents where the margin is full, crop or shrink first, or the number will be unreadable.
No. You receive a new document; the one you uploaded stays as it was.
Yes — choose the pages to number, so a cover page can stay clean.
Yes: they are drawn into the page content, not added as a viewer overlay.