sudo apt remove okular

 $ sudo apt remove okular
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  ardour-data ardour-video-timeline cairo-dock-alsamixer-plug-in
  cairo-dock-animated-icons-plug-in cairo-dock-cairo-penguin-plug-in
  cairo-dock-clipper-plug-in cairo-dock-clock-plug-in cairo-dock-core
  cairo-dock-dbus-plug-in cairo-dock-desklet-rendering-plug-in
  cairo-dock-dialog-rendering-plug-in cairo-dock-dnd2share-plug-in
  cairo-dock-drop-indicator-plug-in cairo-dock-dustbin-plug-in
  cairo-dock-folders-plug-in cairo-dock-gmenu-plug-in
  cairo-dock-icon-effect-plug-in cairo-dock-illusion-plug-in
  cairo-dock-impulse-plug-in cairo-dock-keyboard-indicator-plug-in
  cairo-dock-logout-plug-in cairo-dock-mail-plug-in
  cairo-dock-messaging-menu-plug-in cairo-dock-motion-blur-plug-in
  cairo-dock-musicplayer-plug-in cairo-dock-netspeed-plug-in
  cairo-dock-plug-in-data cairo-dock-plug-ins cairo-dock-powermanager-plug-in
  cairo-dock-quick-browser-plug-in cairo-dock-recent-events-plug-in
  cairo-dock-remote-control-plug-in cairo-dock-rendering-plug-in
  cairo-dock-rssreader-plug-in cairo-dock-shortcuts-plug-in
  cairo-dock-showdesktop-plug-in cairo-dock-showmouse-plug-in
  cairo-dock-slider-plug-in cairo-dock-stack-plug-in
  cairo-dock-switcher-plug-in cairo-dock-system-monitor-plug-in
  cairo-dock-systray-plug-in cairo-dock-terminal-plug-in
  cairo-dock-tomboy-plug-in cairo-dock-toons-plug-in
  cairo-dock-weather-plug-in cairo-dock-wifi-plug-in cairo-dock-xgamma-plug-in
  carla-lv2 carla-vst dpf-plugins-common dpf-plugins-dssi dpf-plugins-ladspa
  dpf-plugins-lv2 dpf-plugins-vst fonts-yrsa-rasa gir1.2-gmenu-3.0
  gir1.2-handy-0.0 gnome-power-manager gnome-shell-extension-prefs
  gnome-tweaks gnote harvid libayatana-appindicator3-1 libayatana-indicator3-7
  libetpan20 libgpaste11 libhandy-0.0-0 libkf5jsapi5 libkf5kexiv2-15.0.0
  libkf5threadweaver5 liblockfile-bin liblockfile1 libmarkdown2
  libokular5core9 libprojectm2v5 libqm-dsp0 libqmobipocket2 libsmf0
  libvamp-sdk2v5 libxdo3 libzeitgeist-2.0-0 lsp-plugins-jack
  lsp-plugins-ladspa lsp-plugins-lv2 lsp-plugins-vst nautilus nautilus-data
  okular-extra-backends projectm-data python3-cffi python3-jack-client
  python3-ply python3-pycparser qtspeech5-flite-plugin
  ubuntustudio-lowlatency-settings ubuntustudio-performance-tweaks
  vamp-plugin-sdk xdotool
Use 'sudo apt autoremove' to remove them.
The following packages will be REMOVED:
  okular
0 upgraded, 0 newly installed, 1 to remove and 2 not upgraded.
After this operation, 15,2 MB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 456234 files and directories currently installed.)
Removing okular (4:19.12.3-2ubuntu1) ...
Processing triggers for desktop-file-utils (0.24-1ubuntu3) ...
Processing triggers for mime-support (3.64ubuntu1) ...
Processing triggers for hicolor-icon-theme (0.17-2) ...
Processing triggers for gnome-menus (3.36.0-1ubuntu1) ...
Processing triggers for man-db (2.9.1-1) ...
Processing triggers for bamfdaemon (0.5.3+18.04.20180207.2-0ubuntu2) ...
Rebuilding /usr/share/applications/bamf-2.index...