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Add Watermark to PDF Online Free — PDF Watermark Tool

Watermarking PDFs is one of the most common ways to protect documents, assert ownership, and communicate document status. Whether you need to stamp "CONFIDENTIAL" across a contract, "DRAFT" across a proposal, or your company name across a portfolio, PDFSlick's free online watermark tool lets you do it in seconds — no software to install, no account to create, and no files ever sent to a remote server.

Fully Customizable Text Watermarks

PDFSlick gives you complete control over your watermark appearance. Type any text you want — a single word, a phrase, or even a date. Adjust the font size from a subtle 20px to a bold 120px. Set the opacity anywhere from 10% (barely visible) to 100% (fully opaque). Pick any color using the color picker to match your brand or choose a neutral gray for a classic watermark look. These controls let you create watermarks that are authoritative without being distracting.

Four Position Options

Different documents call for different watermark placements:

Diagonal — the classic watermark style. Text is rotated 45 degrees and placed at the center of each page. This is the most commonly used position for "CONFIDENTIAL", "DRAFT", and "SAMPLE" watermarks because the diagonal text is visible on every part of the page without obscuring any single section.

Center — text is placed horizontally at the center of each page. Good for short status words or company names when you want a clean, non-rotated appearance.

Top — text is placed near the top of each page. Ideal for document classification labels, date stamps, or version numbers that should be visible at a glance when scrolling through a multi-page document.

Bottom — text is placed near the bottom of each page. Useful for copyright notices, confidentiality statements, or page-level annotations that should stay out of the way of the main content.

How PDF Watermarking Works

When PDFSlick adds a watermark to your PDF, it uses the pdf-lib open-source library to draw text directly onto each page of the document. The watermark becomes part of the PDF's page content — it is not a separate layer that can be easily removed. The text is rendered with the exact font size, color, opacity, and rotation you specified. This means the watermark is visible in every PDF viewer, in print, and in screenshots. The original text and images in your PDF remain fully intact and selectable.

Common Use Cases for PDF Watermarks

Businesses use watermarks to mark internal documents as "CONFIDENTIAL" or "INTERNAL USE ONLY" before distributing them. Legal professionals watermark draft contracts and pleadings to prevent premature reliance on unsigned versions. Photographers and designers watermark PDF portfolios to deter unauthorized use of their work. Teachers watermark exam papers and answer keys. Real estate agents watermark property listings shared with prospective buyers. In all these scenarios, a visible watermark communicates important context about the document's status and intended use.

100% Private — No Server Upload

PDFSlick processes your PDF entirely inside your web browser using JavaScript. Your file is never transmitted to any server. This makes PDFSlick safe to use with sensitive documents — legal briefs, medical records, financial statements, HR documents, and other confidential PDFs can all be watermarked without any data leaving your device.

Related PDF Tools

After watermarking your PDF you may also want to compress it to reduce file size for email, merge it with other documents, or split it into separate files.