The official Ubuntu repositories are maintained by a group of human beings. Because they need time to check each application for updates and pack them for distribution, they tend to be generally behind the curve. Stability is slightly less important.

To get bleeding-edge versions, you can build them from source or download the package from their site (if they offer one, I see Okular doesn't), but there is a way that you can use apt for certain programs. Launchpad allows users to create their own apt repositories that packages can be downloaded from. Packages downloaded from these are likely to update much faster than the Canonical archives because the developer will update it themselves when they make it.

Unfortunately, although Okular is on Launchpad, it doesn't have this. https://launchpad.net/okular

You might be able to convince them to make one, but otherwise I think activating the pre-released packages, as Radu proposed, is your best option.