When comparing Sumatra PDF vs Okular, the Slant community recommends Sumatra PDF for most people. In the question“What are the best PDF readers?” Sumatra PDF is ranked 1st while Okular is ranked 3rd. The most important reason people chose Sumatra PDF is:
Sumatra is available for free, licensed under GPL with source code available on [GitHub](https://github.com/sumatrapdfreader/sumatrapdf).
Question Ranking
Pros
Pro Free and open source
Sumatra is available for free, licensed under GPL with source code available on GitHub.
Pro Portable
The application consists of a single file that can be run without installation. You can put it on an external device, such as an usb thumb stick and run it on any Windows machine from the thumb stick.
Pro Extensive keyboard shortcuts
Pro Multilingual
It's available in 69 languages.
Pro Elegant interface
Pro Low resource usage
Pro Starts quickly
Pro Trim margins
Easily trim margins either automatically or manually for easier reading
Pro Free and open source
Pro Supports touch interaction
Pro Table selection
Cons
Con Lacking in features
Sumatra aims for simplicity at the expense of functionality. For example, there's no way to annotate PDFs or edit them.
Con Windows only
Con Poor HiDPI support
You may have to tinker with QT__SCALE_FACTOR environment variables to get the desired size and not blurry content (this is a bug; see https://bugs.kde.org/show_bug.cgi?id=362856 and https://bugs.archlinux.org/task/54688)