FineDocs
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Watermark a PDF

Stamp DRAFT, CONFIDENTIAL or a name diagonally across every page of a PDF, free. Honest about what a watermark does and does not prevent.

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Short wins. The mark is scaled to fit the page diagonal, so a long phrase comes out small.

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Above about 30 the text underneath becomes hard to read on screen.

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#888888

Mid grey disappears into most documents. Red reads as a warning and fights with body text.

Results appear here. Nothing is uploaded.

    How it works

    Helvetica Bold is embedded once, then each page receives a single rotated text operation with an alpha value. The size is derived from that page's own diagonal divided by the number of characters, so the same setting looks right on A4 and on a widescreen slide instead of overflowing one and getting lost on the other. Because rotation happens about the anchor point, the anchor is offset by half the rotated extent to leave the mark centred.

    What to watch out for

    A watermark is a label, not a lock

    It is drawn into the page content like any other ink, so anyone with a PDF editor can select and delete it in about a minute. It stops nothing. What it does is make a copy obviously a copy, which is a real purpose and a much smaller one than people expect.

    The text underneath stays perfectly selectable

    Marking a document does not touch the text already in it. Anyone can still select, copy and search every word, because the watermark sits on top rather than replacing anything. If the goal is to stop copying, this is the wrong tool and the honest answer is that no PDF setting reliably achieves it.

    A diagonal mark is hardest to read over body text

    Forty-five degrees is the convention because it crosses the reading direction, which is exactly why it interferes most with paragraphs. On a text-heavy report a horizontal mark at low strength is usually kinder; the diagonal earns its place on slides and drawings.

    Limits

    Files up to about 100 MB work reliably. Beyond that, the ceiling is your device's memory rather than any rule we impose — the work happens on your own machine. Tested in Chrome 140, Firefox 143, Safari 18.

    What a watermark is actually for

    It answers one question: if this page turns up somewhere it should not have, is it obvious where it came from and what state it was in?

    That covers most of the real uses. A quotation stamped DRAFT cannot be waved around as final. A specification stamped with a client’s name makes a leaked copy traceable to whoever it was sent to. A print stamped CONFIDENTIAL tells a person who finds it on a printer tray that it should not be there.

    None of those depend on the mark being hard to remove, which is fortunate, because it is not.

    Being straight about what it does not do

    It does not stop copying. The words already in the document remain selectable and searchable; the mark sits over them and changes nothing underneath.

    It does not stop removal. The mark is ordinary page content, and a person with a PDF editor can delete it in about a minute. Tools that promise a “permanent” watermark are either flattening the page to an image — destroying the text in the process — or overstating what the format allows.

    It does not stop screenshots, printing or retyping. If the requirement is that someone must not read the content, the answer is a password, and there is a tool for that on this site.

    Choosing strength and angle

    The two settings interact more than they look.

    Strength below about 8 percent tends to vanish when printed on a laser printer, which renders light greys harshly. Above about 30 percent it starts fighting the text for attention on screen. Fifteen is a good default for a document meant to be read.

    Angle is conventionally 45 degrees, and the reason is that it cuts across the direction of reading — which is also exactly why it is the most disruptive choice over dense paragraphs. On a report full of body text, zero degrees at low strength usually reads better. The diagonal comes into its own on slides, drawings and anything with large empty areas.

    Why the size is not a setting

    A fixed point size that suits A4 is far too large on a slide and lost on a poster. The mark is therefore scaled from each page’s own diagonal, divided by how many characters have to fit along it — which is also why a short word looks bold and confident while a long sentence comes out small and apologetic.

    If your mark is coming out smaller than you wanted, shorten the text rather than looking for a size dial.

    Nothing is uploaded

    The document is opened, drawn on and re-saved in a Web Worker in your browser. Documents worth marking as confidential are, by definition, documents worth not sending to someone else’s server first.

    Your files never leave your browser. Last updated 2026-08-02.