Why iLovePDF Desktop is our fastest app: the move to Qt 6

What is iLovePDF Desktop? iLovePDF Desktop is the offline PDF editor for Windows and Mac from iLovePDF. It lets you read, edit, convert, compress, merge, and sign PDFs on your own computer, without uploading your files. After rebuilding it with Qt 6 and QML, it now runs about twice as fast as before and is the fastest app in the iLovePDF family.

Most people meet iLovePDF in a browser tab. But a lot of PDF work doesn't belong online: a contract you'd rather not upload, a 300-page report on a slow connection, or a folder of scans you need to process on a train.

That's what iLovePDF Desktop is for. And over the past few years, our desktop team rebuilt it from the interface up. Qt, the framework the app is built on, recently published the story as part of its Built with Qt series. Here's our side of it, and what it means for the way you work with PDFs.

Key takeaways

• iLovePDF Desktop is an offline PDF editor for Windows and macOS that processes files on your own computer.
• We rebuilt the app with Qt 6 and QML, which made it about 2x faster overall.
• The app now uses the full power of your processor, so the faster your computer, the faster your tasks finish.
• The new interface is smoother and more intuitive, with dark mode and animations.
• 97 to 98% of the code is shared between Windows and Mac, so both versions get the same features at the same time.
• Faster development means new tools and improvements reach you sooner.

What iLovePDF Desktop does

iLovePDF Desktop brings the tools you know from the website to your computer, with one key difference: your files are processed locally. Documents stay on your machine, which is why it's the natural choice for confidential files and for anyone who works offline.

Inside the app, you'll find a PDF reader, printing options, and tools organized by what you want to do:

• Organize PDF. Merge, split, and rearrange pages.
• Optimize PDF. Compress heavy files and run OCR on scanned documents so you can search and copy their text.
• Convert to and from PDF. Turn Office files into PDFs, convert PDFs to Word and other formats, or create PDF/A files for long-term archiving.
• Edit PDF. Add text, watermarks, and page numbers, and update document metadata.
• PDF security. Protect, unlock, and sign your documents.

If you're not sure whether to work online or on your computer, our guide on choosing where your PDF files are processed walks through both options.

Why we rebuilt iLovePDF Desktop

The first version of iLovePDF Desktop was built with Qt 5 and an older interface toolkit called Qt Widgets. It did its job well. It was fast at processing files and ran on both Windows and macOS from a single codebase.

But at iLovePDF, usability comes first, and expectations for desktop software kept rising. People wanted an interface that felt as polished as the apps they use every day.

The plan started small. "Make the interface look nicer" quickly grew into a longer list: dark mode, animations, smoother transitions, and quicker answers to user feedback. As Alexander Giss, Technical Lead of our desktop team, put it, at that point it no longer made sense to keep building on the old toolkit.

So the team set three goals:

1. A modern interface that is smoother, more intuitive, and easier on the eyes.
2. Faster development, so new features and fixes ship sooner.
3. No compromise on speed or platforms, keeping fast file processing and full support for Windows and Mac.

Why we chose Qt 6 and QML

Instead of patching the old interface, the team migrated to Qt 6 and rewrote the interface entirely in QML, Qt's declarative language for building user interfaces.

There was one catch: at the start, nobody on the desktop team knew QML. Rewriting the whole interface took time, but it also cleared out old bugs and limitations, and left the app with a much clearer structure.

QML describes an interface as items inside other items, so developers can picture exactly how a screen is put together. It also separates the interface from the engine that processes your files. One developer can build a new screen while another works on the processing behind it, and the two pieces fit together.

What changed for you

It's about twice as fast

To ship the new interface sooner, the team first left the processing engine as it was. Eventually they rewrote that too, improving core operations like file conversion and OCR.

The result is roughly 2x faster application performance. In tests on the interface itself, rendering with QML ran about five to six times faster than the old version.

The app now spreads its work across all the cores in your processor. In practice, that means a more powerful computer gets through big tasks even faster, with no setting to change.

A smoother, more intuitive interface

Our users aren't all PDF experts, and they shouldn't need to be. The new interface was designed so anyone can find the right tool and get a result quickly.

Qt 6 also brought better images, animations, shadows, and rendering, which is what makes the app feel fluid rather than functional. And yes, dark mode is now part of it.

The same app on Windows and Mac

With Qt, 97 to 98% of the code is shared between the Windows and macOS versions. Only a handful of platform-specific details differ.

For you, that means no second-class version. Whether you're looking for a PDF editor for Windows or a PDF editor for Mac, you get the same tools, the same interface, and the same updates at the same time.

Your files stay on your computer

The move to Qt 6 didn't change one of the app's most important traits: documents are processed locally. Qt also handles the app's local data storage, so your recent files and settings are available even without a connection.

The app connects to the internet for things like signing in to your Premium account and, if you choose to contact our support team, sending the details they need to help you.

What changed behind the scenes (and why it matters)

A faster team means a better app, so the internal gains matter too.

New features arrive sooner. When our designers have an idea, the team can build a working demo in a few hours. A shared library of interface components makes new screens quicker to build and easier to keep consistent.

New developers get up to speed 3x faster. iLovePDF's Operations Officer and one of iLovePDF's founding members, says moving to QML improved onboarding and training for new developers up to three times.

A small team keeps pace. The desktop team builds both the interface and the processing engine itself, without relying on third-party viewers. Even so, it now ships new features at the same speed as our other product teams.

As Sergio Aguilera, Senior Software Engineer, summed it up:

The biggest win isn't any single number. It's flexibility. Qt 6 means we aren't locked into past decisions about which platforms we support or what kind of experience we offer, so the app can keep evolving with what you need.

Desktop, web, or mobile: which iLovePDF should you use?

All three share the same tools and the same goal. They just suit different moments.

Choose iLovePDF Desktop when you work with confidential documents, large files, or batches of PDFs, or when you need to work offline. It's also the fastest option, especially on a powerful computer.

Choose the website for a quick task on any device, with nothing to install.

Choose the iLovePDF Mobile App when the document is on your phone, or when you need to scan a document and send it by email.

If your whole team handles PDFs every day, iLovePDF for Business brings all of them under one account, with shared access, admin controls, and a single bill.

FAQ

Can I use iLovePDF offline?

Yes. iLovePDF Desktop processes your files on your own computer, so you can work on PDFs without an internet connection. Download it for Windows or Mac from the iLovePDF Desktop page.

Is there an iLovePDF app for Mac?

Yes. iLovePDF Desktop is available for both macOS and Windows. Because almost all of the code is shared between the two versions, Mac and Windows users get the same features and updates.

Is iLovePDF Desktop faster than the online version?

Usually, yes. Files don't need to be uploaded or downloaded, and the app uses the full power of your processor. After the rebuild with Qt 6, it's the fastest of all iLovePDF products.

Is iLovePDF Desktop a good offline PDF editor for confidential files?

Yes. Because documents are processed locally, they don't leave your computer. That makes it a good fit for contracts, financial records, HR files, and anything else you'd rather not upload.

What is iLovePDF Desktop built with?

iLovePDF Desktop is built with Qt 6, a cross-platform development framework, and its interface is written in QML. You can read the full story in Qt's iLovePDF case study.

A faster PDF editor, on your own computer

In summary: we rebuilt iLovePDF Desktop with Qt 6 and QML to give you a smoother interface, about twice the speed, and the same experience on Windows and Mac. Your files are still processed on your own computer, and new features now reach you faster than before.

It's the same iLovePDF that millions of people use every day for quick fixes and that international companies rely on for document management, PDF processing, and e-signatures, now at its fastest on your desktop.

Work on your PDFs offline, at full speed, on Windows or Mac

Download iLovePDF Desktop