One of the exciting new programs introduced in KDE 4.0 is a unified document viewer called Okular.
Based on the solid foundation of KPDF from the KDE3 era, Okular became a document viewer with many more features and support for a large number of formats. At the time I wrote about it in my blog post about KDE4.0.0 it supported 28 file types. In version 0.8.2 (part of KDE 4.2.2) as shipped with Kubuntu Jaunty it supports 45 file types. Note that these numbers may vary greatly with the number of packages supporting various file types installed and that some of the supported types are just compressed versions of others.
Here is what it (a later version: 0.14.1, the screenshots were lost and needed to be re-done) looks like displaying in order: a PDF file, a JPG image, an OpenDocument document and a Comic Book Archive comic.