How to preview PDF files in dolphin

I use Dolphin 21.12.3 on Ubuntu 22.04.
Dolphin cannot visualize pdf files (the pdf icon appers instead) while it can visualize many graphical formats: is that as it should be, or in principle I should be able to preview also pdf files?
In case what could be wrong?
Thanks, Marco

You can select in the options whether to preview specific formats

You may be missing the kdegraphics-thumbnailers package, which provides PDF previews.

if you’re truly on Ubuntu (not Kubuntu) and you manually installed KDE packages on top of the default stuff, you’re likely missing a lot. See Distributions/Packaging Recommendations - KDE Community Wiki for a list of things you’ll want to install.