This tool writes page numbers onto the pages of an existing PDF. You choose where they go (top or bottom, left, centre or right), how they read (1, Page 1, Page 1 of N or 1/N), the number to start from, the font size, the distance from the edge in millimetres, and which pages get a number. A live preview shows the number on the real page before anything is written.
The numbers are added as real text in a standard PDF font, on top of the existing page content, so they print crisply and can be selected like any other text. Pages that are turned sideways in the file are handled, so the number sits upright where you expect it. If a PDF is password-protected you can enter the password; the numbered copy is saved without one.
Limits: the number is drawn over whatever is already in that spot, so if a page has a footer there, pick another position or a larger margin. The tool doesn't renumber the PDF's internal page labels (the numbers some readers show in their toolbar), and it doesn't do legal Bates numbering with prefixes.