Okular enables to quite simply add a proper digital signature, see https://docs.kde.org/stable5/en/okular/okular/signatures.html#adding_digital_signatures https

Okular enables to quite simply add a proper digital signature, see https://docs.kde.org/stable5/en/okular/okular/signatures.html#adding_digital_signatures https://docs.kde.org/stable5/en/okular/okular/signatures.htm...