When using Ubuntu, I cannot read CHM and EPub documents, even if I have okular-extra-backends and libchm1 installed. Why?
Ubuntu (thus Kubuntu as well) packages of Okular are compiled without support for these two formats. The reason is explained in this Launchpad report.
Why are the speak options in the Tools menu grayed out?
Because you don’t have a speech service on your system. Install the Qt Speech library and they should be enabled
Some characters are not rendered and when enabling debug some lines mention ‘Missing language pack for xxx’
Install the poppler-data package