There is a whole industry built around this type of function and numerous service providers that charge a fee per document to do this type of conversion. You are better off buying than building it on your own.
The idea of converting Everything is fundamentally a fool's errand as you would need a single program that could render every file type ever created (in essence recreating every piece of software that ever wrote a data file AND recreating ever version of each). Also, not every file format has a format that has a direct rendered form. For example, what do you do with a database file, a DLL,an XML file, a WAV file?
If you are looking for something that does a reasonable job for a large number of formats, there are two main players with OEM toolkits, but both are extremely expensive and neither supports the Java platform directly. I use the former if you have any additional questions.
Stellent (now Oracle) OutsideIn: http://www.oracle.com/technologies/embedded/outside-in.html
Autonomy KeyView: http://www.autonomy.com/content/Products/idol-modules-keyview-viewing/index.en.html