This is a PDF backend for Okular using MuPDF. MuPDF performs much better than the default poppler backend. It becomes default upon installation and the only way I know of to make poppler default again is to uninstall it. It is possible to select the backend upon opening a PDF file by ticking "Show backend selection dialog".

The original source code can be found at: svn://anonsvn.kde.org/home/kde/trunk/playground/graphics/okular/mupdf