PDF Watermark Tool - Add Watermarks to PDF Online

A PDF watermark is a semi-transparent visual identifier overlaid on document pages, commonly as text (such as "Confidential", "Copyright", "Internal Use") or images (such as a company logo). Watermarks do not cover or modify original content; instead they sit on top of pages at low opacity, serving as identification without affecting readability.

Similar to a stamp on paper documents, digital watermarks serve three main purposes: copyright protection (claiming document ownership), confidentiality labeling (indicating sensitivity level) and source tracing (identifying distribution channels). Watermarks are a simple and effective deterrent and information marker in government documents, design drafts, contract drafts and financial reports.

Our PDF Watermark tool is based on browser Canvas and pdf-lib technologies, rendering watermark layers locally for each PDF page. You can quickly generate watermarked PDFs without uploading documents to a server.

This tool supports both text watermarks and image watermarks, with flexible control over position, opacity, rotation angle and size.

Text watermarks are suitable for fixed labels such as "Confidential", "Internal Use" or "Draft". You can set font size, color, opacity and rotation angle. We recommend setting opacity between 0.2~0.4 so the watermark is visible without obscuring the main content.

Image watermarks are ideal for company logos or signature images. After uploading a PNG or JPG image, you can control its page proportion via the scale setting. We recommend using transparent PNG logos placed in corners or at the center.

For layout, the tool offers single position and full-screen tiling modes. Single position works well for logos or small marks; full-screen tiling is better for copyright protection against screenshots or photocopying. Page ranges support syntax such as 1,2-3,4, allowing watermarks on specific pages only.

This tool uses a pure frontend architecture. PDF parsing, watermark rendering and new document generation all happen inside your browser. Files are never uploaded to any server, and watermarked results are kept only in local memory and released when the page is closed.

All operations rely on pdf-lib and browser-native APIs, so no account registration or network connection is required. If you are handling documents containing business secrets or personal privacy information, we recommend using the tool in an offline environment and downloading or clearing results promptly after processing.