Merge PDFs in the browser with JavaScript (no uploads, no server)

In this post I'll show how to merge PDF files entirely in the browser using PDF.js and pdf-lib — no server, no file upload, no backend. Everything runs on the user's machine, which is great for privacy and for keeping hosting costs at zero (it's just a static site).

Why process PDFs on the client?

Most "free" PDF websites quietly upload your documents to their server, which:

Exposes private/sensitive files to third parties

Imposes size limits

Merge PDFs in the browser with JavaScript (no uploads, no server)

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