Watermark PDF
Mark a document’s status on every page. Set the text, opacity, angle, size, colour and position, then download — the stamping happens on your device, not on a server.
How to use Watermark PDF
- Upload your PDF.
- Type your watermark text.
- Adjust opacity, rotation, size, colour and position.
- Click “Apply watermark” and download.
About Watermark PDF
The mark is written as real page content rather than laid over the top as an annotation. pdf-lib appends a short run of operators to each page’s content stream — set the alpha, set the font and colour, rotate the coordinate system, draw the string — so the text becomes part of the page in the same way the original text is. It therefore survives printing, flattening, re-saving in another application and conversion to an image, none of which is reliably true of a stamp that lives in a separate annotation layer.
Long strings at large sizes used to run clean off the sheet, so the size is fitted before anything is drawn. Text metrics scale linearly with font size, which means the rotated bounding box can be computed exactly and the requested size reduced in a single pass until the string sits inside the page with a little room to spare. The practical effect is that “STRICTLY CONFIDENTIAL — DO NOT CIRCULATE” at 120 points on a narrow page shrinks to fit rather than showing you its middle six letters. Every page is fitted against its own dimensions, so a landscape appendix is handled correctly.
Getting the appearance right is a trade-off in two directions. Too faint and the mark vanishes in a photocopy, which is the situation it exists for; too strong and it fights the text underneath. For most documents a large diagonal string somewhere between 10% and 25% opacity, crossing the page at around 45 degrees, is the balance that works — unmissable while leaving the body readable. A small solid label along the top or bottom suits marks meant to be read rather than merely noticed: a version tag, a recipient’s name, a case reference. Pale red and pale blue tend to survive photocopying better than a grey of the same lightness.
Be clear about what this achieves. A watermark is a label and a deterrent: it declares status, it makes the source obvious in a screenshot, and it makes casual reuse awkward. It is not access control and should never be treated as such — anyone with an editor can strip added content, and the words underneath were never protected to begin with. Two practical limits: the mark goes on every page rather than a chosen subset, and the built-in font covers Latin letters, digits and common punctuation, so Arabic, Chinese, Cyrillic and Greek will not render.
Frequently asked questions
Can I control the opacity and the angle?
Yes. Opacity runs from 5% to 100% and the font size from 12 to 140 points, while a centred mark can be rotated anywhere between 0 and 90 degrees. Colour is a free choice, and the text can sit diagonally across the middle or along the top or bottom edge.
Does the watermark go on every page?
Every page, and each is measured against its own size — so a landscape fold-out inside a portrait report receives a mark scaled for that page instead of one that overruns the edges. There is currently no way to stamp only a subset.
Can someone remove the watermark?
Yes, given the right software. Added page content can be edited out by anyone with a full PDF editor, and the text beneath a stamp is not obscured in the file, only visually. Treat it as a label rather than as protection; use encryption when a document genuinely must not be read.
Is my document uploaded to be watermarked?
No, which is rather the point: a file worth marking CONFIDENTIAL is a file worth not sending to an unknown server. The text is drawn into the document inside this tab and the result downloads straight to your machine.
Will it show up when the page is printed or photocopied?
It prints, because it is part of the page rather than a screen overlay. Photocopying is less forgiving — very low opacity can be dropped altogether by a machine set to high contrast — so raise the opacity if the paper copy is what matters.
Can I use a logo image or non-Latin text?
Neither at present. The mark is text drawn with a standard built-in font, which covers Latin characters, numerals and ordinary punctuation. Scripts outside that range and image logos are not supported.
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