How to add page numbers to a PDF

Page numbers are the sort of thing nobody thinks about until they are missing. Then someone says "look at page seven" and there is a long silence while everyone counts.

Adding them to a document you are still writing is easy — every word processor does it. Adding them to a PDF that already exists is a different job, and it comes up constantly: a report assembled from several sources, a scanned bundle, a contract with appendices from three different people.

What is actually happening

A PDF has no idea it has pages in the sense of numbered pages. It has a list of pages, in order, and that is all. There is no header, no footer and no field that updates.

So numbering a finished PDF means drawing the number onto each page — placing text at a specific coordinate, in a specific font, on top of what is already there. Nothing else is touched. The existing content, text and images all stay exactly as they were, with a small piece of new text added on top.

That has two consequences worth knowing. The numbers are permanent once the file is saved, and they are drawn *over* the page, so a number placed where there is already content will sit on top of it.

The four decisions

Where. Bottom centre is the safe default and the most common in print. Bottom right suits documents that will be flicked through, because the eye lands on the outer corner. Top corners work for reference material where someone is looking things up.

What it says. Just the number is right for most documents. "Page 3" adds nothing but is common in reports. "Page 3 of 12" is genuinely useful for anything printed or emailed, because it tells the reader whether they have the whole thing — a real benefit when documents get forwarded and pages go missing.

Where the numbering starts. Two separate questions hide here, and people conflate them constantly:

• Which physical page gets the first number (the cover usually should not).
• What that number is (often 1, sometimes 47 because the document continues from another volume).

Whether it is printed double-sided. If so, an outer-corner number has to swap sides on alternate pages, or every second number lands in the binding.

The cover page problem

A report with a title page almost never wants "1" on the cover. It wants the cover clean and page 2 to be page 1.

That is one switch, and it does the arithmetic for you: page one is skipped, and the page after it starts at 1 rather than 2. It sounds obvious but plenty of tools get it wrong by simply starting the count at page 2, which gives you a document whose first numbered page says 2.

The related detail is what "of N" means when a cover is skipped. On a 12-page document with an unnumbered cover, the correct total is 11 — the number of pages actually being numbered — not 12. A reader looking at "Page 11 of 11" should be looking at the last page.

Starting at a number other than 1

This comes up more than you would think:

• A chapter that continues from a previous file.
• A document whose front matter was numbered separately in roman numerals.
• A bundle where the first section was already numbered by someone else.
• Legal exhibits that continue a run.

Being able to say "start at 47" saves reassembling the whole document to get the numbering right.

Facing pages

For anything printed double-sided and bound, this matters. On a right-hand page the outer edge is the right; on a left-hand page it is the left. A number fixed to the right lands in the gutter on every second page, half-swallowed by the binding.

Switching on facing pages mirrors left and right placements on alternate pages so the number is always on the outer edge. Centre placements are unaffected, which is one reason bottom-centre is the low-risk choice.

Numbers over dark backgrounds

If your pages have a coloured footer, a photograph or a dark banner, a dark number placed there simply disappears.

Two fixes: change the number's colour, or put a small white pill behind it. The pill is more reliable because it works regardless of what is underneath, though it is visible as a shape. On a document with a consistent design, changing the colour is tidier.

Rotated pages

A PDF page can carry a rotation flag — very common in scanned bundles where some pages went through the feeder sideways. A tool that ignores rotation places the number in unrotated coordinates, which puts it along the side of the page as the reader sees it, rotated 90 degrees.

Correct behaviour is to measure the page as it is displayed and place the number accordingly, so a rotated page gets its number in the bottom corner *as seen*. Worth checking on the output if your document has mixed orientations.

Preview before you commit

Nine positions, several formats, a colour and a size is a lot of blind choices, and most tools make you convert first and look afterwards. Page Numbers draws a live page beside the settings that updates as you change them, including the facing-page spread, so you can see where the number lands before spending anything.

Order first, numbers second

One practical warning. If you are assembling a document from several files, merge them and get the order right before numbering. Numbers are drawn onto pages permanently, so reordering afterwards leaves you with a document whose numbers are in the wrong sequence — and removing them means going back to the originals.

Assemble, check the order, then number. In that sequence it takes two minutes.

One last check before you commit

Numbers are drawn onto the page permanently, so it is worth spending thirty seconds on the preview.

Look at the busiest page in the document — the one with a table running to the bottom, or a full-page image. That is where a number lands on top of content rather than in clear space, and it is the only page where the position setting is genuinely tested.