I use Okular to view PDF documents on Ubuntu 18.04. If I have multiple PDFs open at the same time, each of them creates a new item in the Ubuntu Dock. This quickly messes up my dock. In addition, there is no preview available. I often end up ALT + TAB'ing into many of the documents first before I find the one that I want to look at.
All other applications that I regularly use are grouped automatically. If, for example, I have two Firefox windows open at the same time, they are grouped together in the dock and in the Alt + TAB switch panel. There is also a preview shown for each Firefox window. This makes it easy to select the desired window quickly.
My question: Is there an option to tell Ubuntu that it should group Okular documents in the same way as Firefox and basically everything else?