Add page numbers prints a number onto every page of a PDF, in a position and format you choose, directly into the page content rather than as a separate overlay that depends on the viewer. Once added, the numbers show up the same way in any reader and on any printout.
What to choose, and why it matters
Position usually follows convention: bottom centre or bottom right for most documents, top for some academic or legal formats. Format matters for anything someone will reference later: "Page 3" is fine for a short document, but "3 of 40" tells a reader how much is left, useful for a report that might be printed and read away from a screen. Starting number matters when a cover page or table of contents shouldn't count as page 1, a common request: numbering can start from a chosen page rather than the very first one, so the content itself begins at "1."
When plain numbers aren't what you need
Plain sequential numbers restart at 1 for every document and say nothing about which document a page came from. That's a problem for a specific case: a bundle of exhibits, contracts or records submitted together, where every page across every file needs a unique, traceable identifier, such as ABC000001, that survives even if pages are separated later. That's what Bates numbering is for, a different, more rigid scheme used in legal and compliance filings; see Bates numbering explained and Bates numbering if that's the actual requirement rather than ordinary page numbers.
Combining with a header or footer
If a page number needs to sit alongside a date, a document title or a confidentiality notice, rather than stand alone, Add header and footer places all of that together along the top or bottom of each page in one pass.
Questions
Can I start numbering from a page other than the first?
Yes, choose a starting page so earlier pages, such as a cover sheet, stay unnumbered or are skipped from the count.
Can I make it say "Page 3 of 40" instead of just "3"?
Yes, that format is one of the available options, and the total page count updates automatically to match the file.
What's the difference between this and Bates numbering?
Plain page numbers restart at 1 for each document. Bates numbering assigns a unique, continuous identifier across a whole set of files, used mainly for legal and compliance records; see the guide linked above.
Will this affect the existing content on the page?
No. The number is added into the page without changing the existing text, images or layout underneath it.