From your screenshot, the "diagonal lines" are present outside of the kpdf
window. So this is unlikely to be kpdf's fault. More likely a mis-configuration within Xwindows, and more specifically, your video card and its driver.
But you have not given us any
information about your linux distro, video chipset or window-manager. Linux isn't windows, and even if you were running windows, don't you think you should be telling us whether it's 3.1, 98, XP, 2K, NT, or vista? They are all different, so is linux.
So, nobody can help you until you learn to help yourself.
Please read all
of this link: http://www.catb.org/~esr/faqs/smart-questions.html
Then you'll be welcome back here with a proper question