Privacy-First PDF Merging: Why I Built merge-pdf.app
We’ve all been there. You have three different PDFs, maybe a cover letter, a CV, and some certifications - and you need them in one single file. The “old” way to do this usually involved searching for “Merge PDF” on Google, clicking the first link, and uploading your sensitive documents to a random server in the cloud. You get your file back, but at what cost? Who has that data now? Is it sitting in a temp folder on a server in another country? Will they delete it? Will they use it to train AI?
I decided to build a better, more private way to handle this common task.
The Reasoning: Privacy by Default
Current pdf-merging/combining services online have a “middleman” problem. For a simple task like joining two documents, your data shouldn’t have to travel to their servers. My goal was to create a tool where your files never leave your computer. Most online PDF tools are “Server-Side.” You upload -> they process -> you download.
merge-pdf.app is 100% “Client-Side.” You load the app -> your browser processes -> you save the merged file. By using the browser as the engine, we eliminate the risk of data breaches on the server because, quite simply, there is no data on the server to steal.
How It Works (The Tech Bit)
The site is built using Vue 3 and Vite, keeping the interface snappy and the footprint small. But the real heavy lifting is done by a library called pdf-lib.
When you select your files, the app doesn’t “upload” them in the traditional sense. Instead:
The browser reads the files into local memory (as ArrayBuffers).
pdf-lib intercepts these buffers and modifies the PDF structure directly in your browser’s RAM.
It stitches the pages together and generates a new Blob.
When you click “Merge,” you’re just saving that Blob to your hard drive.
Because I’m using Vite PWA, after you’ve visited the site once, it even works offline. You can turn off your Wi-Fi, merge your documents, and it works perfectly. That’s the power of modern web standards!
Protecting Your Privacy
I wanted to be as transparent as possible about how your data is handled. Here is the privacy “stack” for this project: No Tracking: There are no invasive analytics tracking you. No Storage: Since there’s no backend database or file storage, I couldn’t keep your documents even if I wanted to. Static Hosting: The site is served as static files. When you request the page, the server just hands you the HTML/JS/CSS and then gets out of the way. Your device now has everything it needs to perform the merging. Open Logic: The processing logic happens in your browser. If you’re tech-savvy, you can open the Network tab in your DevTools and see for yourself: when you merge a PDF, there is zero network traffic.
Wrapping Up
This project was born out of a personal need for a tool I could trust. It’s fast, it’s free, and most importantly, it treats your data with the respect it deserves.
If you want to try it out, head over to the merge-pdf.app and merge a few files. I don’t think the “Cloud” is always the best place for your private documents.
Happy merging!