Merging PDFs in the browser with pdf-lib (no server upload)

Most online PDF mergers upload your file to a server. For sensitive documents, that's a problem.

Approach

Use pdf-lib in the browser:

1. Read files with File.arrayBuffer()
2. PDFDocument.load() each source
3. copyPages() into a new PDFDocument
4. save() and download via a Blob URL

The PDF never needs to leave the user's device for this flow.

Verify privacy

Open DevTools → Network, merge a test PDF, and confirm there's no upload request carrying the file body. After the app loads, you can even try offline.

Try it

I packaged this (merge, split, and more) in PDFCraftify:

• Merge tool: https://pdfcraftify.com/merge-pdf
• Guide: https://pdfcraftify.com/guides/merge-pdf-without-uploading

Tradeoffs

• Browser memory limits very large jobs
• Password-protected PDFs must be unlocked first
• Not a replacement for full desktop DTP

If you build similar tools, what edge cases bite you most? Comments welcome.