Why PubConvert Processes Files in Your Browser

Most online file converters upload your documents to their servers for processing. PubConvert is different — your files never leave your computer. Here's why we built it this way and what it means for you.

How Most Converters Work

Typical online converters follow this flow:

1. You upload your file to their server
2. Their server processes the file
3. You download the result
4. Your file sits on their server (for how long? who knows?)

This means your documents — which might contain sensitive business information, personal details, or proprietary designs — are stored on someone else's server.

How PubConvert Works

PubConvert's entire conversion engine runs in your web browser:

1. You select your .pub file
2. Your browser reads the file locally
3. Our JavaScript code parses and converts the file
4. The result is generated on your device
5. You download directly from your browser

At no point does your file leave your computer. There's no upload, no server processing, no cloud storage.

Why Client-Side Processing Matters

Privacy

Your documents stay on your device. Period. We can't see them, we can't store them, and we can't share them. This is especially important for:

• Business documents with confidential information
• Files containing personal data (addresses, phone numbers)
• Proprietary designs and branding materials

Speed

No upload or download wait times. The conversion starts instantly because there's no network transfer. This is especially noticeable with larger files or slower internet connections.

Reliability

No server outages, no queue, no "please try again later." If your browser works, PubConvert works.

The Technical Challenge

Building a file converter that runs entirely in the browser is significantly harder than a server-side solution. We had to:

• Parse the OLE2/CFB binary format in JavaScript — the same complex container format used by older Microsoft Office files
• Decode the Escher drawing layer — Microsoft's drawing format that stores shapes, text boxes, and images
• Handle the Quill text format — Publisher's text formatting system with its own chunk-based structure
• Generate multiple output formats — PDF, DOCX, PPTX, and HTML, all from pure JavaScript

The result is about 6,000 lines of TypeScript that can parse and render Publisher files without any server involvement.

The Trade-Off

The one trade-off is that very large or complex files may take a moment to process since your device is doing the work. But for the vast majority of Publisher files, conversion is nearly instant.

Try It Yourself

Upload a .pub file and see the conversion happen instantly — right in your browser.