Install libokular5core8 by entering the following commands in the terminal:
sudo apt update sudo apt install libokular5core8
Description:
libraries for the Okular document viewer
This package contains libraries used by the Okular document viewer. . This package is part of the KDE graphics module.
Homepage: http://www.kde.org/
Version: 4:17.12.3-0ubuntu1
Section: universe/libs