I can digitally sign odt files in libreoffice but when I try to do the same with pdf files the field for the gpg credentials is empty.

I am using LibreOffice with openSUSE. When I sign an odt file the window with my gpg credentials comes up an everything works fine. However if I try the same with a pdf file the same window comes up but the gpg credentials are missing and consequently I cannot sign the file. The pdf document is opened read only as requested and it says it is opened read only for signing. Why is this different? can I enter somehow the gpg credentials manually?

OK I found a bug report about this. In the end they write that you can only sign pdf files with X509 certificates and not with GPG. I find it odd that you can sign any open office format with PGP but not pdf files. I don’t need a X509 certificate since I don’t fun a web server but I use PGP for encrypting and signing emails and I started to sign documents. I hope this will be made possible in libreoffice soon.