Hello,
I would like to know which Linux distro is suggested to try some Okular development, that is, opening the source code, modify it and compile the application.
Is it important to have a KDE distro?
Thanks in advance for any advice or opinion.

Hi,

no, doesn't matter. There's no "KDE distros", just distributions shipping KDE as default desktop environment (or not). You can use about anything. Even non-linux operating systems.

Greetings,
Sven

shouldn't be better to have a distribution with most libraries pre-installed?

Why care? It takes few seconds to pull them in with a package manager.

As scummos any distro should work, if you have any problem getting the needed packages for your distro drop by the #okular irc channel of the freenode.net network and we'll give you a hand (it's much easier to give help live in IRC and here with post after post)