How to Add Page Numbers to a PDF (and Why the Old Ones Stay)

Some documents arrive without page numbers, and a document that gets printed, signed and filed without them is a document that loses its place. Others arrive with page numbers that are wrong, because they were numbered before three files were merged together.

Adding them is a small job. The interesting part is knowing what the tool does and does not fix.

What you can choose

The Add Page Numbers tool lets you set four things:

• Where the number goes - bottom or top, and left, centre or right. Six positions in all.
• How big it is - 8 to 18 points.
• Whether to show a total - just 7, or 7 / 42.
• Where the numbering starts - 1 by default, anything you like.

That last one is the one people need and rarely think of.

The starting number is the whole point of the tool

A document with a cover sheet wants the cover unnumbered and the first content page as page 1. Set the start to 1 and the cover gets a 1 like everything else. Set the start to 2 and the cover is 1.

And if your document already has its own numbering, the start number is how you keep it. A 40-page report whose pages are numbered 1 to 40, with a cover sheet in front, is 41 sheets: the cover is page 1 and the report's own page 1 is sheet 2. If you want the report's own numbering to survive, you set the starting number to 0 - the cover becomes 0 and the first content page becomes 1.

This is the trick that makes the tool useful on real documents rather than only on blank ones.

The total counts the last page, not the number of pages

The "of Y" format is worth reading carefully, because it is not what people expect.

The total is the last page number. So a 10-page document that starts at 5 reads:

5 / 14
6 / 14
...
14 / 14

Not "5 / 10" through "14 / 10", which is what you get if the total is taken to be the page count. The total follows the start, so the last page always reads "N / N", whichever way you numbered it.

If you want the familiar "1 of 42" on a 42-page document, leave the start at 1 and everything lines up.

The old numbers do not go away

This is the limit that catches people, and it is worth being blunt about:

Adding page numbers draws new numbers on top of the page. It does not renumber, remove or replace the ones that are already there.

If your document prints "Page 14 of 40" in its own footer, the result has two numbers on every page: the original, and the new one the tool draws in the margin. That is not a bug in the tool - the tool does exactly what it says. It is a consequence of the fact that a printed number is just text in the page, and the tool has no way to know that some text in the footer is a page number.

So there are two routes, and they are not equally good:

• Renumber at the source. If the document comes from a word processor or a design tool, change the numbering there and export again. You get one set of numbers, correct, in the font and position you chose.
• Strip and re-add. Remove the old numbers first, then add the new ones. Which is what removing the text layer is not - but a PDF editor that can delete a footer rectangle will do it, and then the tool adds clean numbers to what is left.

If the document has no numbers yet, none of this applies and the tool is all you need.

The numbers do not move the content

The numbers are drawn in the margin, 24 points from the edge, in a plain sans-serif face. They are added as a drawing instruction on the page - the content itself is copied, not re-rendered.

That means the text, the images and the resolution are exactly as they were, and the file size barely changes.

It also means the number is ordinary text: it can be selected, searched and copied, which is what you want for a searchable document.

One practical caveat: 24 points from the edge is a small margin. On a page with a busy footer - a letterhead, a decorative rule, a page border - the number can land on top of it. Look at one page before you number the whole document.

The merged-document problem

Worth its own paragraph, because it is the most common reason people reach for this tool at all.

You merge three documents. The merged file has pages 1 to N. The second document started at page 14 and the third at page 5 - and after merging they are pages 5, 6 and 7 of the new file. Merging destroys the original page numbering, and no tool can recover it, because the numbers were text in the pages and merging does not rewrite text.

The fix is to number last, and to number only if the document needs it:

1. Merge the files.
2. Then add the numbers to the merged document, with the start number you want.

Numbering before the merge is the mistake - you end up with three sets of numbers that all claim to be page 1.

A short checklist

• Number the document AFTER merging, not before.
• Set the start number to match the numbering the document already has - 0 to skip a cover, or the first number of the original.
• The total is the last page number, so "5 / 14" is correct for 10 pages starting at 5.
• Old printed numbers stay. Renumber at the source, or strip them first.
• Check one page for overlap - the margin is 24 points, which some footers reach into.
• The content is not re-rendered, so nothing degrades and the size barely moves.