If you're going to need the content searchable you'll need to setup a third party module such as the Venexus Search, it should index those files for you and allow people to search through them. That would be seperate from the IFrame functionality though, getting the files to load in an IFrame shouldn't be too hard if you configure a seperate page for each document. Though the search results will most likely link directly to the files, not to the IFrame pages themselves.