Add Watermark to PDF Online
Stamp custom security watermarks, draft notices, or company stamps across all PDF pages in your browser.
How to Add Watermark to PDF Online Free
When you add watermark to PDF documents with DocxLab, our browser engine injects a semi-transparent vector text layer into each PDF page content stream. This ensures the watermark overlays all content crisply without rasterizing the underlying text or blowing up the file size.
Select PDF Document
Upload your PDF. The entire file is read directly in your browser memory without being transmitted to any remote servers.
Customize Text & Appearance
Type your custom watermark text (e.g. DRAFT, CONFIDENTIAL, COPY), adjust typography size, transparency opacity, and diagonal slant.
Download Stamped Document
Instantly download your watermarked PDF with indelible vector security stamps applied uniformly across all pages.
Privacy & Technical Note: Watermarks are embedded using native Helvetica standard font vectors with calibrated alpha transparency, keeping the output compact and universally printable.
Frequently Asked Questions about PDF Watermarker
Can someone easily erase or select the watermark text?
The watermark is written directly into the graphic state stream of each PDF page alongside existing content. While anyone with an advanced PDF editor could modify raw streams, casual readers cannot simply select or delete the stamp.
Will adding a watermark make my PDF file size significantly larger?
No. DocxLab uses standard PDF vector fonts that do not require embedding bulky font subsets or rasterizing pages into images. The file size increase is typically less than 2 kilobytes total.
Can I adjust the transparency so the document text remains readable underneath?
Yes. The opacity slider allows you to dial in transparency between 5% and 80%. The default 25% provides clear watermark visibility while leaving background text 100% legible.
Are my proprietary or financial PDFs kept private?
Completely private. The PDF parsing, font embedding, and file generation run entirely inside your browser sandbox. No file data is sent across the Internet.