Add Watermark & Page Numbers

How to use it

1. Drop a PDF onto the box above, or click Choose a file.
2. Turn on Text watermark, Page numbers, or both.
3. For the watermark, set the text and then adjust position, colour, size, opacity and — for the centred position — the angle.
4. For page numbers, pick a format and corner, and choose whether to skip the first page.
5. Optionally limit which pages are stamped in Apply to pages.
6. Click Apply to PDF and download the result.

How it works

Text in a PDF is not pixels. Each page carries a content stream — a short program of drawing instructions — and adding a watermark means appending a few more instructions to it: set this font at this size, set this colour and this transparency, move to this point, rotate by this much, show this string. Nothing already on the page is touched, which is why the file barely grows and quality is unaffected.

Two details take more care than the drawing itself.

Rotated pages. A PDF page can carry a /Rotate value telling readers to turn it a quarter or half turn before display. The drawing commands, however, always run in the page’s own unrotated coordinate space. On a page marked as rotated 90°, asking for “bottom centre” in the space you can see is a different point from “bottom centre” in the space the text is drawn in. The tool converts between the two, and adds the page’s rotation to the text angle so the stamp reads in the same direction as the page content. Without this, watermarking a mixed portrait-and-landscape scan puts text sideways and half off the page.

Font encoding. The fourteen standard PDF fonts are guaranteed present in every reader, which is why they need no embedding and cost no file size. They are also WinAnsi-encoded and physically cannot represent characters outside the Latin range. Your text is checked before any drawing starts and the specific character at fault is named, rather than letting the font encoder throw partway through a hundred pages.

Positioning also accounts for the size of the text itself: a corner stamp is inset by half its own width and height so that no part of it hangs over the page edge, and the rotation pivot is offset so an angled watermark stays centred rather than swinging away from the middle.

Tips

• Preview the result in the PDF Viewer before circulating it. Opacity that looks right as a number often reads differently over a dense page.
• For a diagonal “CONFIDENTIAL” stamp, the centre position at 45° and around 18 per cent opacity is the conventional look, and 48 pt suits A4 and Letter.
• A watermark stating something specific — “DRAFT — NOT FOR CIRCULATION”, a date, a recipient’s name — deters sharing far more effectively than a generic one.
• Number and watermark in a single pass rather than running the tool twice. Two passes means two rounds of re-saving for no benefit.