Is there an app that is like good reader that will allow you to index your dropbox files. For example if I want to search for all docs that contain a certain word. (not just PDFs). It should be similar to how spotlight on the desktop works.

No, and probably never going to happen.

In order to do that the app would have to download all the files, then index them, then constantly monitor for changes, download those and index. That kind of defeats the whole online storage meme.

Or, Dropbox would have to do the indexing on it's site, and then provide an API to access that index. Which of course would mean that the Dropbox site would have to peek inside your supposedly encrypted and secure files. Not a good way to attract businesses.

So all you can do is search those unencrypted file names.

Sorry.