Building a Browser-Based PDF Watermark Tool with pdf-lib and QPDF

In this article, we'll explore how to implement a pure client-side PDF watermarking tool that runs entirely in the browser. This tool can add both text and image watermarks to PDF documents, making it perfect for branding, copyright protection, and document identification. Why Browser-Based PDF Watermarking? Traditional PDF watermarking typically requires: Uploading sensitive documents to a server Trusting third-party services with your files Potential privacy and security risks Browser-based processing solves all these issues: ✅ Files never leave your computer - complete privacy ✅ No document transmission over the network ✅ Instant processing with no upload delays ✅ Zero server costs ✅ No risk of documents being stored or misused The Challenge: PDF Watermarking PDF watermarking is complex because: Watermarks must appear on every page Text watermarks need to support multiple languages (especially CJK characters) Watermarks should be semi-transparent and optionally rotated Image waterma