Why number your pages
Page numbers make long documents easier to read, discuss and check. Lawyers, auditors and tender committees refer to pages by number, universities usually require numbered theses and assignments, and a numbered bundle shows quickly if a page is missing. When you merge several PDFs into one file, adding page numbers at the end gives the whole bundle one clear order.
Position, format and size
You can place the number at the top or bottom of the page and align it left, centre or right. Four formats are available: just the number, Page 1, 1 / 10 and Page 1 of 10. The text size can be set from 6 to 36 points; 10 or 11 suits most A4 documents. The number is placed a small distance from the edge, so it stays clear of the normal printing margin.
Skipping the cover and starting at any number
Many documents should not show a number on the cover or the table of contents. Set "Start on page" to the first page that should carry a number; earlier pages are left as they are. "First number" sets the number printed on that page, so you can continue the numbering of an earlier part, for example start at 25 for the second volume of a file. The total in the "of" formats is the last number printed.
Rotated and mixed page sizes
PDFs often mix portrait and landscape pages, or contain pages that were rotated after scanning. The tool works out how each page is shown on screen and places the number so it is upright and in the chosen position on every page. Pages of different sizes each get the number in the same relative place.
Private and free
The PDF is opened and changed in your browser with pdf-lib, and the preview is drawn with pdf.js. Nothing is uploaded, so confidential reports and contracts stay on your device. The numbers are added as real text in a standard font, so they print sharply and do not change the rest of the page. Arabic numerals in Eastern style are not offered yet, because the standard PDF fonts do not include them.