Indexing such documents requires the optional wordprocessor plugin that is only available for purchased products. Once you have that you need to use the -n option as described in the manual to invoke it during a walk.
We have a commercial version 2.5 with the wordprocessor plugin.
Those documents are indexed, but during the display of search results, only the name of the document is displayed without any description. Is there a way to display a abstract for these documents too?
It should just display if the document wasn't empty. Click "match info" to see what text was extracted from the documents.
Also, are you using the default abstracts that come from the beginning of the document (<abstract $Body 180>) or hit-in-context abstracts (<abstract $Body 180 smart $query>)? Perhaps you want the latter if you're not using it already.