If I understand you correctly, you want the users to be able to read the documents, but not to save them locally?
Usually, this use case is pretty difficult in a web environment, as the web browser has to download the information in order to display it in the first place.
You might want to consider developing a java applet or Adobe Flash component that prevents casual "right-click" saving (take a look at the web-based song lyric websites). Alternatively, render the protected documents to an image which will at least prevent simple copy/paste operations on the text. Finally, I understand there's a specific PDF format which allows this use case, but I'm unfamiliar with the exact config required.
Thanks,
Mike