How to restore Okular default (toolbar) settings

I've somehow managed to remove the toolbar and menu-bar from Okular. After I've found no way to reactivate them from "outside" – sice I can't click on Options anymore – I've tried to reinstall a clean version after removing it with apt-get remove --purge okular. However, it didn't work, the tool- and menu-bars were still unavailable. I also looked for any configuration files in the home directory, without success. How should I proceed now in order to restore a clean Okular.