Number every page – choose the format, the position and the first number.
Share the numbered PDF as a HelpRange link and see time spent on every page, by every reader, with an alert when they open it.
Page numbers make long documents easier to discuss ("see page 14") and are expected in contracts, theses, reports and due diligence documents.
Any text with {n} for the page number and {total} for the page count, e.g. "Page {n} of {total}", "{n}" or "{n}/{total}".
Yes – set the first number, e.g. 3 if the PDF continues another document.
No – it is processed in memory and not stored.