Various web services can open Microsoft Office files with ease, but what about files created with LibreOffice? The good thing is, you can also read ODT document in your browser as well.
One of the new applications introduced with KDE 4 was Okular. KDE 3 had a PDF viewer named KPDF, but Okular aims to be a complete document viewing solution, supporting many different file types. Okular is fast-loading and works in any operating system and desktop environment that can run KDE applications.