Kleopatra is a free and open source certificate Manager and unified Crypto software for Linux. Using this application you can manage X.509 and OpenPGP certificates in the GpgSM keybox. Not only this you can also retrieve certificates from LDAP servers. It is a kde project and released under GNU General Public License v2.0 or later.
Install Kleopatra on Ubuntu Linux
Kleopatra is a available from flatpah as a flatpak package file. First you need to install the latest version of flatpak and flathub on your system and you need to restart your system after that. Follow below link.
After that run below Kleopatra flatpak installation command. It will install the Kleopatra app on your system.
flatpak install flathub org.kde.kleopatra
You can start Kleopatra using this command.
flatpak run org.kde.kleopatra
And uninstall Kleopatra using
sudo flatpak uninstall org.kde.kleopatra