Many time ago I could sign PDF documents with X509 certificates using LibreOffice. IIRC I kept the certificate in the Firefox keychain and LO could see and use it without problems. Now I can’t.
When clicking to sign the selection dialog appears empty:
I checked in Firefox and the certificate is imported.
Maybe the Firefox keychain password dialog is hidden behind the selection one? If so, I can’t see a way to put it in front to add the keychain password.
Using F34 and libreoffice-core-184.108.40.206-2.fc34.x86_64 on Wayland.