No certificate visible for signing PDF

Using LibreOffice on Fedora 28:

I try to digitally sign a PDF document. To do this

  • I select File | Digital Signatures | Sign Existing PDF…
  • then I choose to open a PDF generated with LibreOffice Writer;
  • then I select the Sign Document button in the blue bar;
  • the Digital Signatures pop up window opens. Here I select the Sign Document… button;
  • the Select Certificate pop up window opens, but there are no certificates visible.

However, when I use a similar procedure to sign an .odt or .odg document, I do see my OpenPGP certificate.

Am I doing something wrong, or is this a bug?

Apparently only x.509 certificates are supported for PDF signing.
Bug 115884 - PDF signing should mention it only works with x509 certificates
The resolution of that bug report is to update the LO 6.1 documentation to reflect this limitation.

Also mentioned here when the feature was first announced:
LibreOffice 4.5 to provide PDF signing and timestamping

Have not see anything about adding OpenPGP support to this feature.

If this solves your issue, please check the checkmark at left.