openSUSE Tumbleweed LibreOffice 7.6.4.1 With Draw I try to digital sign a pdf with digital signature > signing an existing pdf > sign the document > select the document > start the certificate manager > sign the document > select the certificate The window of the list of the certificates from kleopatra is empty. Thus, I can't select a certificate. The option "digital signature > digital signature" for a .dot file works well. The windows "select the certicate" supplies all the Kleopatra certificates. Thus, I can select a certificate and sign the document.
Unfortunately the PDF standard doesn't allow OpenPGP signatures. You can only sign PDF files with X.509 certificates. There's a ticket to add a UI hint that only X.509 keys will work. bug 115884: PDF signing should mention it only works with x509 certificates As a workaround you can use KDE-Kleopatra (or directly GPG) to create a signature for the PDF as a separate SIG file. For that open KDE-Kleopatra and choose File->Sign/Encrypt. For further help ask at KDE or GPG.