PowerPoint presentations text not searchable

I am trying DT, and I am very impressed. I run into a problem today, though. Trying to import PPT files, I have found that some files are searchable, DT recognizes all the words and classifies them properly. But some files show 0 words, and DT doesn’t seem to be able to access any information in them. I can see the presentation with all the slides in the viewing pane, but the search engine can’t see the words…
I will appreciate any suggestions.

The example you’ve provided (via a support ticket) isn’t fully supported by Spotlight’s plugin for MS Office documents, the only solution is to convert the documents to a recent PowerPoint format.