How to add page numbers to a PDF

The position of a page in the file starts at one for the very first sheet, whatever that sheet is. The number printed on a page is whatever the document’s own convention says it should be. These agree only when a document begins numbering on its first physical page, which formal documents rarely do.

Take a report with a cover, an inside title page and a two-page contents section. Conventionally the body starts at page 1, and that body page is the fifth page in the file. If you stamp every page starting at 1, the cover gets a 1 and the body page that should read 1 reads 5 — every cross-reference in the document is then wrong by four.

The fix is the two settings working together. Restrict the stamped pages to 5 onward so the front matter is left unnumbered, and set the starting number to 1 so the first stamped page reads 1. The printed sequence then matches the document’s own convention, and a reader asked for page 20 finds the page marked 20.

If you want the front matter numbered too, the conventional treatment is Roman numerals on those pages and Arabic from the body onward. That is two runs: one over the front matter with the Roman format, one over the body with the starting number reset to 1.

The starting-number setting exists mainly for packs assembled from separately produced parts. If section one ends on page 30, stamping section two with a starting number of 31 makes the pack read continuously even though it is several files, or was until you merged it.

Work out the numbers before stamping anything, because each part needs its own run with its own start value, and an error in one shifts every part after it. Counting pages per section first and writing down the start values takes a minute and saves redoing the whole pack.

If the parts will be merged anyway, the simpler route is to merge first and number the combined document once. Then the sequence is continuous by construction, and you only have the front-matter offset to think about. Numbering before merging only makes sense when the parts are produced by different people or must also stand alone.

Numbers are drawn on top of the page, and the tool has no knowledge of what is already there. A document with an existing footer, a bottom-banner watermark, or a marginal note in the corner you chose will get a number overlapping it. Pick a corner that is empty across the whole document rather than empty on page one.

The margin setting is the other half of this. Too small and the number sits in the region a printer may not be able to reach or a binding may swallow — most desktop printers have an unprintable margin of a few millimetres. The 28-point default clears that comfortably. Increase it if the document will be bound or trimmed.

Mixed page sizes need a thought too. Positions are computed relative to each page’s own dimensions, so a merged A4-and-Letter document gets numbers correctly placed on every page but not at an identical distance from the top of the stack, since the pages differ in height. If uniformity matters, normalise the page size before numbering.

Finally, the stamped number becomes page content like any other text. It appears in text extraction and in search, and it does not renumber itself if pages are later added or deleted — a document you stamp and then edit will have numbers that no longer match, and the correct fix is to re-stamp from the unnumbered original.