How I Built a 100% Client‑Side PDF Suite with WebAssembly and Web Workers (Zero Cloud Storage)

Description and use

A fully client‑side PDF suite built with WebAssembly and Web Workers that processes files locally, ensuring privacy and instant performance without cloud reliance.

Problem

Online PDF tools upload sensitive documents to third‑party servers, exposing them to privacy risks, network latency, and high cloud costs.

Outcome

PDFBlack delivers 40+ PDF tools (merge, compress, Bates numbering, etc.) entirely client‑side, achieving instant processing, zero upload, and no cloud costs.

Workflow

• Select PDF file in browser
• Upload file to Web Worker via postMessage
• Worker loads PDF with pdf-lib
• Perform operations (merge, compress, reorder, numbering)
• Worker posts modified ArrayBuffer back
• Main thread creates Blob and triggers download
• Revoke object URL to free memory

Evidence

PDFBlack: an open‑source suite of 40+ PDF tools that processes 100% of your documents locally in your browser.

Source

All document processing runs inside dedicated Web Workers.

Source

The project is live at pdf-black.com, and you can explore the codebase on our GitHub repository.

Source