About mergepdf.dev

Why we built this

A few years back, a colleague of ours was putting together a contract for a new client. Nothing unusual — just combining a few PDFs before sending them off. He used one of those popular online merge tools, uploaded the documents, and got his merged file. Job done.

Except a week later, he got an email from the tool's support team saying there'd been a "data incident." His files — including the contract with the client's personal details — had been exposed. The tool had promised to delete files after processing. They hadn't.

That stuck with us. It's such a mundane task — merging PDFs — and yet the standard way of doing it online carries a real privacy risk that most people don't think about. So we built something different: a tool that never sees your files in the first place.

What we actually built

mergepdf.dev runs entirely in your browser. When you select PDFs, they load into your browser's memory — not our servers. The merging happens locally using pdf-lib, an open-source JavaScript library. The result downloads directly to your device. We never see your files, because they never travel anywhere.

You can verify this yourself: open Developer Tools (F12), go to the Network tab, and watch what happens when you merge. You'll see the initial page load, then nothing. No uploads. No API calls. Just your browser doing the work.

1. PDFs load into your browser's memory
2. JavaScript reads and combines them locally
3. The merged PDF is created on your device
4. Your browser downloads the result

What makes us different

Built on open source

We're built on pdf-lib, an MIT-licensed library created by Andrew Dillon. It's the reason we can do all of this in a browser without a server. The source code is public — you can read it, audit it, and confirm for yourself that it doesn't send data anywhere.

We're grateful for the open-source community that makes tools like this possible.

How we think about this

Privacy is the default, not a feature

We didn't add privacy as a selling point after the fact. The architecture — client-side processing, no backend, no file storage — means privacy is baked in. We couldn't collect your files even if we wanted to.

Honest about what we do track

We use Google Analytics to understand how people use the site — page views, which features get used, that kind of thing. No file contents, no document metadata. We're upfront about this in our privacy policy.

Simple on purpose

We've resisted adding features that would complicate the interface. The tool does one thing well: merges PDFs. That's intentional. Most people just need to combine a few files quickly — they don't need a full PDF editor with a learning curve.

Kept running honestly

Non-intrusive ads keep the lights on. No paywalls, no data selling, no "premium" version that holds features hostage. If you find the tool useful, the best thing you can do is let the ads load.

Under the hood

For the technically curious:

• Frontend: Vanilla JavaScript — no framework, no bloat
• PDF processing: pdf-lib 1.17.1, running in a Web Worker
• Styling: Custom CSS with CSS Variables
• Fonts: Plus Jakarta Sans & Inter via Google Fonts
• Hosting: Static site — no backend server at all
• PWA: Installable, works offline via service worker

What's coming

We're working on a few things:

• Page-level preview before merging
• Rotate individual pages in the merge interface
• PDF splitting (separate tool)
• Compression while merging
• Dark mode

Everything will keep the same principle: your files stay on your device.

Say hello

If something's broken, confusing, or you just want to tell us the tool saved you from a $18 in-flight Wi-Fi charge — we'd genuinely like to hear it. Head to our contact page.

Help us keep going

mergepdf.dev is free and always will be. If it's been useful:

• Share it with someone who needs it
• Link to it from your site or blog
• Send us feedback — it genuinely helps
• Let the ads load (they're non-intrusive, we promise)

Thanks for using it.