How Plain Works
Plain processes PDF files entirely in your browser. No files are uploaded to any server. This page explains the technical architecture and shows you how to verify it yourself.
In Simple Terms
When you use Plain, your PDF files never leave your device. All processing happens inside your web browser using built-in technologies. You can verify this by checking your browser's network activity or by using Plain while offline.
Plain is a browser-based PDF toolkit. Unlike traditional online PDF services that require you to upload files to remote servers, Plain runs entirely within your web browser. Your files are processed locally on your device, and no data is transmitted over the internet.
What "Client-Side" Means
"Client-side" refers to code that runs in your browser rather than on a remote server. When you load Plain, the application code is downloaded once. After that, all PDF operations happen locally on your machine.
This is fundamentally different from server-side processing, where files are sent to a remote computer, processed there, and sent back. With client-side processing, your files never travel across the network.
No Servers, No Uploads
Plain does not operate any file-processing servers. When you select a PDF file, it is read directly by your browser using the File API. The file data stays in your browser's memory, is processed locally, and the result is made available for download—all without network transmission.
This architecture eliminates several categories of risk: data breaches, unauthorised access, third-party storage, and compliance complications. Your files remain under your control at all times.
Browser Technologies Used
Plain leverages modern browser capabilities to perform PDF operations locally:
- JavaScript — The primary programming language for browser applications, handling user interactions and orchestrating PDF operations.
- WebAssembly (Wasm) — A binary format that allows near-native performance in the browser. Used for computationally intensive PDF processing tasks.
- File API — Standard browser API for reading files selected by the user without uploading them.
- Blob API — Used to construct the output PDF file and create a download link.
These are standard web technologies supported by all modern browsers. No plugins or extensions are required.
Offline Mode Explained
Because Plain processes files locally, the tools continue to work even when you're offline. After the initial page load, no network connection is required.
This is possible because all necessary code is loaded when you first visit the page. The application uses a Service Worker to cache assets, enabling offline use. You can disconnect from the internet, process your PDFs, and download the results—all without any network activity.
Offline functionality is a natural consequence of client-side architecture. If the processing required servers, offline mode would be impossible.
How to Verify This Yourself
You don't have to take our word for it. Here's how you can confirm that Plain doesn't upload your files:
Verification Checklist
- 1
Open DevTools Network tab
Press F12 or right-click and select 'Inspect', then click the Network tab.
- 2
Process a PDF file
Use any Plain tool (e.g., Merge PDF) while watching the Network tab.
- 3
Observe network activity
You will see no file uploads to any server. Your PDF data stays local.
- 4
Test offline mode
Disconnect from the internet after loading the page. The tools still work.
This level of transparency is intentional. We believe users should be able to verify privacy claims, not just trust them.
Plain's architecture is designed around a simple principle: your files should never leave your device unless you explicitly choose to share them. Client-side processing makes this possible.
To learn more about the differences between online and offline PDF tools, see Online vs Offline PDF Tools. To try the tools yourself, visit the Tools page.