To have the latest version of Okular you have 3 options:
Easy Option - Install the latest Kubuntu. Either 11.10 or wait for 12.04. The reason for this will be explained in the other Options.
Intermediate Option - Download the DEB Package of Okular and all of it's dependencies and the dependencies of those dependencies until you have literally downloaded KDE in pieces just to install that since the latest Okular depends on libraries and other packages that also depend on others that need to be a specific version or newer. This versions are not compatible with an older Ubuntu so you would have to start downloading a lot of packages. This in most cases will not work and waste your time since at some point a package might say "Hey I need a newer kernel version of autotool, autoconf, make... and so on." So your chances of having it work there are very difficult.
Difficult Option - Compile the whole thing from scratch. This option will take more experience and a heck of more time to do and at the end it will not guarantee that it will work on the kernel used in Ubuntu 10.10 with the versions of the tools provided in 10.10.
To make matters worse, 10.10 has been discontinued. So try the option everyone has suggested (Install 12.04). If you do not want a heavy system then install Lubuntu or Xubuntu and then install Okular from there but just so you know, you can install Okular very easy and with less download time in Ubuntu 12.04 since it already comes with the QT libraries for it. No need to download them when trying to download Okular.