I built a privacy-first PDF merger in 7 hours — here's the stack and the lessons

Day 8 of building SwapFile.io in public. How pdfunite beats rasterization, why my conversion_jobs table didn't need a migration, and the 50-line Go wrapper that does the heavy lifting.

lunedì 25 maggio 2026 New tab

1,041 words~5 min read

TL;DR

Day 8 of building SwapFile.io (privacy-first image/PDF converter) in public. Yesterday I shipped a feature I needed myself: PDF Merge. Total time: ~7 hours from "do we have this?" to production. Stack: Go + Fiber + PostgreSQL + Next.js 16. The interesting bits are about what I didn't have to write.

Live: swapfile.io/en/tools/pdf-merge

The problem

Most online PDF mergers do something I didn't realize until I tested four of them: they rasterize your PDFs.

I built a privacy-first PDF merger in 7 hours — here's the stack and the lessons

I built a privacy-first PDF merger in 7 hours — here's the stack and the lessons

Related reading

Building Convertify in Public Week 10: PDF Cluster + Blog Launch

ShowDev: I built a 100% local, zero-upload PDF editor using WebAssembly

I tried to build a SaaS. I'm shipping tiny libraries instead.

Months of self-testing: Citations shine, other features remain unproven.

Why I Built a Privacy-First Dev Toolkit

Github Copilot helped us cut down 50-75% time in our e-commerce business

Related reading

Building Convertify in Public Week 10: PDF Cluster + Blog Launch

ShowDev: I built a 100% local, zero-upload PDF editor using WebAssembly

I tried to build a SaaS. I'm shipping tiny libraries instead.

Months of self-testing: Citations shine, other features remain unproven.

Why I Built a Privacy-First Dev Toolkit

Github Copilot helped us cut down 50-75% time in our e-commerce business