I found in a job posting:<p>iPaper is an unusually complex Flash application with many highly technical components.<p><a href="http://www.scribd.com/jobs/7" rel="nofollow">http://www.scribd.com/jobs/7</a><p>So it looks proprietary.
Looks like they started with something like <a href="http://www.swftools.org/" rel="nofollow">http://www.swftools.org/</a> and developed a custom viewer for the swf files.<p>For doc and other formats, one can use openoffice commandline tools to convert them all to pdf.<p>edit: Some history - <a href="http://news.cnet.com/8301-17939_109-9874527-2.html" rel="nofollow">http://news.cnet.com/8301-17939_109-9874527-2.html</a> Scribd initially used the now discontinued flash paper.