okular supports signing. But you have to set up your signing certificate outside it and then point it at the certificate database in the backend settings. Creating a signing certificate in adobe, saving that to a file, registering that file with nsdb, setting nsdb as backend in okular, works. Only have to do the setup obcr, then just works.

also when they see this post

seems so, and the steamdeck too I think macs also have sth like this.