[Zope] TextIndexNG and ExtFile

All, I've got a site with a couple hundred ExtFile objects. I now need to index the content of the various files (word, pdf, excel, ppt). I see that ExtFile doesn't have a PrincipiaSearchSource method so I created one. It returns self.index_html(). When I go back into my catalog and reindex my PrincipiaSearchSource index (a textindexng index), clicking the "Reindex" button opens the ExtFile I'm trying to index. Is there something more to the process of trying to index ExtFiles with TextIndexNG. I've googled around and tried a few things but either they don't work or I get the same results I've just described. Any ideas? Thanks, Tom Palermo