PDF Tools

Add Watermark

Overlays one line of text, such as CONFIDENTIAL or DRAFT, across every page of a PDF. You set the wording, font size (20 to 100 pt), opacity (5% to 100%) and rotation (-90 to 90 degrees); the colour is fixed at mid grey.

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Watermark Text

Font Size: 50pt

Opacity: 30%

Rotation: -45°

How to Use

1Drop one PDF onto the upload area.
2Edit the Watermark Text field (it starts as CONFIDENTIAL).
3Set Font Size (20 to 100 pt), Opacity (5% to 100%) and Rotation (-90 to 90 degrees) with the sliders.
4Click Add Watermark.
5Download watermarked.pdf.

About this tool

Updated September 19, 2026

One line of text, once per page

A single diagonal line of text is drawn across the middle of every page in the document, in grey bold Helvetica.

It is not tiled and not repeated, so you get one mark per page rather than a lattice covering the sheet. You control four things: the text itself, the size between 20 and 100 points, the opacity from 5% to 100%, and the rotation between -90 and 90 degrees. The defaults — CONFIDENTIAL at 50 points, 30% opacity, tilted -45 degrees — are the familiar diagonal stamp, and they are a sensible starting point.

Choosing an opacity you can still read under

Around 20-35% marks the page clearly while leaving the text beneath legible. Higher values start to fight the content.

A watermark has two jobs that pull against each other: it must be obvious enough to register, and faint enough that the document still reads. Opacity is the main lever. If the mark disappears against a dense page, raise the size before you raise the opacity, since a larger faint mark reads better than a small dark one. Very long text is also a problem, because it is drawn as a single unwrapped line and can run past the page edge; short words like DRAFT, COPY or SAMPLE work best.

It marks a document, it does not protect one

The watermark is ordinary drawn content sitting on top of the page, so editing software can remove it.

This is worth being blunt about. A watermark discourages casual reuse and makes a leaked copy identifiable, and that is genuinely useful. It is not a security control, and anyone determined with the right editor can take it off. If the real requirement is that a document cannot be altered or redistributed, a watermark is not the answer. Marking a draft, a sample or a review copy is exactly what it is for.

Only Latin characters will render

The text is drawn with a built-in font that covers basic Latin and common Western European letters, and nothing else.

No font is embedded, so Urdu, Arabic, Chinese, Japanese and similar scripts will not draw correctly and may fail outright. Stick to the Latin alphabet, digits and ordinary punctuation. The mark also lands in the same place on every page and is applied to all of them; there is no way to exclude a cover page or vary the text by page.

A Guide to the PDF Tools on Synthixx and What Each Does Well
Every PDF tool on Synthixx grouped by job, with one honest sentence on each, its main limitation, and a clear list of what the site does not offer.

Features

Text watermark only; image or logo watermarks are not supported here
Font size 20 to 100 pt in bold Helvetica
Opacity slider from 5% to 100% (default 30%)
Rotation from -90 to 90 degrees (default -45)
Watermark colour is fixed grey; there is no colour picker
One PDF at a time, applied to every page, in your browser

FAQ

Can I change the watermark colour or use an image or logo?

No. This tool draws text in a fixed mid-grey and has no colour control or image upload. For putting a logo on pictures, the image tools on this site handle image files, but PDF pages only get text here.

Will the watermark be centred exactly?

It is positioned from the horizontal centre and the vertical middle of each page, then rotated around its starting point. At steep angles or with long text it can end up off-centre or partly outside the page, so try a shorter word or a smaller size.

Can the watermark be removed again?

It is drawn as text on top of the page content, so it is part of the saved file. Keep your original PDF; there is no undo once you have downloaded the result. There is a separate Remove Watermark tool, but its results depend on how the watermark was added.

Are my files uploaded anywhere?

No. The watermark is applied in your browser and the file is not sent to a server for this job.

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