Are my PDFs uploaded to a server?

No. All processing is done locally in your browser using pdf-lib. Your files never leave your device.

Can I control the opacity of the watermark?

Yes. The opacity slider lets you set transparency from 5% (nearly invisible) to 100% (fully opaque). A value around 20–30% is typical for background watermarks.

Is the watermark applied to all pages?

Yes. The text watermark is drawn on every page of the PDF in the same position.

Will the watermark cover the content?

The watermark is drawn on top of existing content. Use a low opacity (e.g. 20%) to keep the original content readable underneath.

What font is used for the watermark?

The tool uses Helvetica, which is a standard built-in PDF font available in all PDF readers without embedding.

PDF Watermark Tool - Add Text Watermarks to PDF Online

Add text watermarks to PDF files in your browser

Upload a PDF, enter your watermark text, and configure font size, opacity, and placement. The watermark is stamped on every page using pdf-lib running entirely in your browser. No server, no upload, no account required.

Common watermark use cases

The most popular watermark labels are CONFIDENTIAL, DRAFT, DO NOT COPY, and company names. A diagonal placement with 20–30% opacity keeps the original content fully readable while clearly marking the document.

Choosing opacity and font size

For background watermarks, set opacity to 15–25% so the text does not obscure the document content. For foreground stamps (e.g. "VOID"), use 70–100% opacity with a smaller font. Font sizes between 36 and 72pt work well for most letter/A4 pages.

Privacy

Your PDF is processed entirely in your browser using pdf-lib. Nothing is sent to any server. Closing the tab leaves no trace.

Watermark legality and document authentication

A text watermark applied by this tool is a visual overlay and is not a cryptographic signature. It can be removed by anyone with PDF editing software. If you need legally binding document authentication, use a digital signature (ISO 32000-1 PDF signatures) or a certified digital certificate instead.

Visible watermarks are appropriate for draft control, internal distribution labeling, and copy deterrence in low-stakes contexts. For high-security document protection, consider document rights management (DRM) solutions.

Diagonal vs. tiled watermarks

The standard diagonal placement (center of page, rotated 45°) is effective for both letter and A4 formats. For long documents you want to watermark more densely, a tiled pattern (watermark repeated across the page in a grid) is more difficult to remove by cropping, since the watermark appears in every part of the page. Adjust font size and opacity downward when using a tile pattern to avoid obscuring the content.

Preserving existing content and annotations

This tool places the watermark as a new page-level content layer. All existing text, images, hyperlinks, form fields, and annotations in the original PDF are preserved. The watermark is added above the original content layer so it is visible, but it does not modify any underlying content streams.