Number every page – choose the format, the position and the first number.
Up to 10 MB and 200 pages.
“Page 1 of 10”, “1”, “1 / 10” – or your own text with {n} and {total}.
Bottom centre is the usual choice; start at 3 if the PDF continues another document.
Every page is numbered in the position you chose.

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.
Page {n} of {total}, {n} or {n}/{total} – or type your own text, e.g. Exhibit A – {n}.Acrobat Reader (the free app) cannot add page numbers – you need Acrobat Pro or a free online tool such as the one above.
Preview cannot number pages. The simplest free ways are this online tool, or – if you have the original Word or Pages file – inserting page numbers there (Insert → Page Number) and exporting a new PDF.
If you only have the PDF, number it here instead of rebuilding the document.
Any text with {n} for the page number and {total} for the page count, e.g. "Page {n} of {total}", "{n}" or "{n}/{total}".
Upload the PDF to this tool, choose the format and position and download the numbered file – no sign-up, no watermark from us.
No – the free Reader cannot edit PDFs. Acrobat Pro can (Edit PDF → Header & Footer), or use this free online tool.
Set the first number so the numbering matches your document; to leave the cover unnumbered, split it off first with the free split PDF tool and merge it back afterwards.
Yes – set the first number, e.g. 3 if the PDF continues another document.
Only for a short time: uploads are deleted right after processing, the result after 30 minutes – or at once with “Delete now”.