When comparing Sumatra PDF vs KDE Okular, the Slant community recommends Sumatra PDF for most people. In the question“What are the best PDF viewers for Windows?” Sumatra PDF is ranked 1st while KDE Okular is ranked 5th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Starts quickly
Pro Free and open source
Sumatra is available for free, licensed under GPL with source code available on GitHub.
Pro Low resource usage
Pro Does not have heavy editor features
Annotations and other heavy features are just not needed in reader.
Pro Extensive keyboard shortcuts
Pro Elegant interface
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 Multilingual
It's available in 69 languages.
Pro Free and open source
Pro Trim margins
Easily trim margins either automatically or manually for easier reading
Pro Featureful
Pro Table selection
Pro Tabbed view option
Pro Supports touch interaction
Cons
Con Windows only
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 Fonts are not smooth enough
Not as smooth as e.g. Adobe Reader. No anti-aliasing
Con Cannot crop empty fields
Just got used to this killing feature on Goodreader on Mac.
Con No XFA Adobe Forms support
Cannot fill PDF Forms created with Adobe.
Con Requires many KDE libraries
Con No middle-mouse auto-scrolling
Instead of scrolling automatically when holding down the mouse wheel and dragging, it instead zooms in or out, in contrast with many other programs.
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)
Con No search results overview
You have to navigate to next/previous hit one by one
Con No "fit to page" option under printing settings
You can only print the content as given so, when you receive a bigger or smaller image thant the default of the printer, you will have to edit it first on other editor.
Con Slow scroll
Its new ultra-slow-scroll for PgUp and PgDn makes it unuseable.