A watermark is the word a document wears on its sleeve: DRAFT across a proposal that is still changing, CONFIDENTIAL across a report that should not travel, a company name across pages that will be photocopied and passed around. Type your text, pick how strongly it should show, and this tool stamps it across every page of your PDF, on your device.
What watermarks are for
Three jobs account for nearly every watermark. Status: DRAFT, PREVIEW or COPY tells anyone holding the pages — today, or in a filing cabinet in five years — exactly what they are looking at, which prevents the classic accident of an early draft being mistaken for the final version. Confidentiality marking: CONFIDENTIAL or INTERNAL USE ONLY sets expectations the moment a page is seen, forwarded or printed; the marking travels with the document in a way an email warning never does. Branding and ownership: your name or company across sample work, teaching materials or a portfolio discourages passing-off and makes the source obvious wherever a page ends up.
Real text, on every page
The watermark is drawn with pdf-lib (an open-source library running locally in your browser) as genuine PDF text — bold Helvetica in a neutral grey-blue — centred on each page and rotated by the angle you choose: diagonal −45° is the classic document stamp, horizontal reads like a banner, and diagonal +45° tilts the other way. Because it is real text, it stays sharp at any zoom, prints crisply, and can be selected like any other words on the page. One honest consequence follows from that, and it matters: someone with a PDF editor can remove a watermark. A watermark deters, labels and discourages — it does not secure. If you need to control who can open the file at all, that is a different job: use the PDF Lock tool to password-protect it.
Choosing opacity and size
Opacity is how hard the stamp leans on the page. Light (15%) whispers — right for branding on finished documents that must stay elegant. Standard (25%, the default) is unmistakable without fighting the text underneath, and is the right choice for most DRAFT and CONFIDENTIAL stamps. Strong (35%) and Bold (50%) make the marking the dominant thing on the page — use them when being noticed matters more than being subtle, such as DO NOT COPY. Font size works with the length of your text: 48 suits a word like CONFIDENTIAL on a normal page, 72 suits a short word like DRAFT, and 36 keeps a long phrase from running off the edges. If a stamp does not sit right, nothing is harmed — your original file is never modified, so adjust and stamp a fresh copy.
Private by design
Like every CalcViso file tool, this one runs entirely in your browser. The file you choose is read by this page, processed on your device, and offered back as a download — it is never uploaded to a server, never stored, and never seen by anyone else. Close the tab and it is gone from memory.
Worked example
Press the sample button to load a 2-page sample PDF created in your browser. Leave the text as CONFIDENTIAL, opacity on Standard (25%), size 48 and direction on Diagonal −45°, then press Add watermark: watermarked.pdf carries the word CONFIDENTIAL in large grey letters across the centre of both pages, readable at a glance but light enough that the pages' own text still reads cleanly through it.
How to use this tool
- Drop your PDF onto the box (or create the sample).
- Type the watermark text — CONFIDENTIAL, DRAFT, your company name, or anything else.
- Choose the opacity: Light for branding, Standard for most stamps, Strong or Bold when the marking must dominate.
- Choose a font size and a direction — diagonal −45° is the classic stamp; horizontal reads as a banner.
- Press Add watermark and download watermarked.pdf; open it and flick through to confirm every page carries the stamp.
Watermark or password? Pick the right protection
The two tools answer different questions. A watermark answers “what is this document, and whose is it?” for everyone who sees it — including people who were never meant to. A password answers “who may see this at all?” Reach for the watermark when the file will circulate openly but must be labelled; reach for the Lock tool when the contents themselves are sensitive. They combine well, too: watermark the pages CONFIDENTIAL first, then lock the watermarked copy with a password, and the file is both labelled and closed. One practical tip for long documents: because the stamp is placed dead centre on every page at one fixed size, it lands consistently even when pages differ — a landscape chart page in a portrait report gets the same stamp, centred on its own dimensions.