When comparing Jarnal (Java, cross-platform) vs KDE Okular, the Slant community recommends KDE Okular for most people. In the question“What is the best software to annotate a PDF?” KDE Okular is ranked 3rd while Jarnal (Java, cross-platform) is ranked 4th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Collaboration over network (although limited)
It is possible to connect multiple Jarnal clients to a single Jarnal server for collaboration on the same document. However, only one person can make changes at a time.
Pro Free and open-source (GPL license)
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 Some actions are not intuitive
Opening a PDF into Jarnal is not intuitive. The only way I found is by using the supplied shell script. I could not find how to do it from within the UI.
Con Written in Java using Swing toolkit
As with most Java apps, the UI looks alien to all operating systems.
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.