Liferay's engineering team has been doing a lot of work on the Document Library for version 6.1. But in one of the recent weekly meetings, a discussion sparked off about the possibility of having some kind of live preview for the Document Library. This is meant in terms of both (1) thumbnails of files in the file listing and (2) previews of the actual document that you can go through without downloading the file. So, after a little toying around, I got a first cut of this working in trunk (see LPS-13145). Both of them still need to be reskinned (our UI guys are great at that), but I thought I would show a few screenshots of what things roughly look like.
For thumbnails (note that the future version will allow you to pick a plaino list view vs. a thumbnail'd view):
Then, you can also go through each page of the document as well (eventually with zooming capabilities):
How does it work in the backend? Well, first, it converts files to PDF format using OpenOffice. So you need to make sure you have that installed. Then, it breaks up the PDF into images -- one for each page. Now, OOTB, it does it using PDF-box. But, ideally, you should install ImageMagick. This is because PDF-box is great for fairly simple PDF documents, but can get a bit gibberish if you use fonts it doesn't know about and things like that. ImageMagick also runs significantly faster. So, all in all, it is much better if you install ImageMagick.