Flash
Sadly (from a purist POV), Webconverger chose to provide Flash viewer due to the fact several compelling Web applications employ Flash technologies.
Despite that Flash is not free, a black hole binary blob and not supportive of Web standards.
In an office or vertical market environments you probably do not require Flash & noisy multimedia.
I do defend the inclusion of Flash in the main trunk of Webconverger because I think for the most part it makes the Web more compelling.
During the browser wars Microsoft made the Web compelling. Thanks Microsoft. 
One has to look at the big picture sometimes. The Web API is the key to unlocking the potential of Free & Open source software to the world.
The included PDF viewer is free software and PDF is an open file format.
Though please think twice about using PDF on the Web! HTML is the best way to store your documents.