Add Page Numbers to a PDF: Position, Start Number, and the Rotated-Page Trap
How to number the pages of an existing PDF online: choose a corner, set a start number such as 101, and avoid the sideways numbers that appear on pages stored as rotated.
Add Page Numbers writes a plain decimal number onto every page of a PDF. You choose the corner, the font size and the first number; everything else is fixed. It does not know about pages stored as rotated, covers that should stay blank, or numbers already printed on the page, and each of those needs a decision from you before you upload.
What the tool writes
Each number is black Helvetica text added to the page content, so it prints and travels with the file in any viewer. There is no font or color option. It is not the page-label setting some readers show in the thumbnail pane, so a viewer that displays "iii" or "A-1" labels will keep showing its own labels.
The form exposes three settings:
- Position: top left, top center, top right, bottom left, bottom center or bottom right. The form default is bottom center. In the API these are the values 1, 2, 3, 7, 8 and 9; 4, 5 and 6 place the number at the left, center and right of the vertical middle.
- Starting number: default 1. The first page gets this value and each page after adds one.
- Font size: default 12, range 6 to 200 on the form. The API does not enforce that range, so stay within it.
The starting number must be a whole number: abc is rejected with a 400 invalid_parameter, while a negative value is accepted and drawn as is (-2, -1, 0, 1 and so on).
The number's anchor is 48 points (two thirds of an inch) in from the page edges, computed from the page's MediaBox size. Digits are written from the anchor toward the right, so "bottom center" puts the left edge of the digits on the center line and a three-digit number ends slightly right of center. "Bottom right" starts 48 points from the right edge and runs toward it, so a three-digit number at 12 pt ends roughly 28 points from the edge. At 12 pt the offset is hard to notice.
A worked example: volume II of a contract
Take a 6-page file, contract.pdf, that continues a 100-page first volume. Upload it to Add Page Numbers, set the starting number to 101, position to bottom right, size 12. In a run on 2026-10-04 against a local build, the output was a 6-page PDF, and extracting its text showed the numbers 101 through 106, one at the bottom right of each page below its body text. Your viewer's rendering may differ in detail; the order and values will not.
Two things to know about that result. The output keeps the input's name (contract.pdf), so rename it before you overwrite the original. And an API request with no position put the number at top right (value 3), not at the form's bottom center. Send position explicitly in scripts.
Order of operations for a packet
The tool numbers every page of the file you give it. It cannot skip a cover or restart halfway. So the order you work in decides the result:
| Goal | Do this |
|---|---|
| One sequence across several files | Merge first, then number the merged file |
| Each part keeps its own numbering | Number each file, then merge |
| Cover stays unnumbered | Split the cover off, number the rest, then merge the cover back |
| Volume II continues volume I | Set the starting number to the next page, as above |
If the pages already carry a printed number, the new one is drawn in addition to it. Running the tool twice on the same file gives two numbers per page: in a test, a second pass with the same position drew the new "1" over the existing "101", so the two overlap. Keep the unnumbered original and always start from it.
How to cut a cover or a section out cleanly, and what the removed pages can leave behind, is covered in Send Only Some Pages of a PDF.
The rotated-page trap
Pages from scanners and phones are often stored with a rotation flag instead of being redrawn. The number is placed using the unrotated page, so on a page stored as rotated 90 degrees it lands on the wrong edge and turned sideways. In the test, a Letter page flagged as rotated 90 degrees and numbered "bottom center" displayed as a landscape page with a tiny sideways "1" at the left edge, about halfway down, not along the bottom.
When you control the order, number first and rotate afterward with Rotate. The rotation applies to the whole page, so the number turns with the text. If a file arrives already flagged as rotated, this tool cannot compensate and there is no setting to correct it; check those pages in a viewer after numbering.
Check before you print
Open the first, a middle and the last page. Look for digits sitting on punch-hole margins, photos or a footer that already holds text. If the file has trailing blank pages, Remove Pages first and number afterward, so the last number matches the last real page. The numbers are part of the page now, so Extract Pages or reordering afterward keeps them with their original pages and the sequence will no longer run in order; renumber from the unnumbered file when order changes.
Only number documents you are allowed to alter, and keep the unnumbered original when a filing process expects an unmarked source. A password-protected file needs its password: the browser page asks for it, and an API call without it gets a 400 password_required ("This PDF is password-protected. Enter its password."), so unlock the file first. No API key is needed to call the tool.