Hi Mobs,
There are quite a few unanswered questions. But, not exactly the easiest task and it will take a fair amount of Javascript coding. If you are doing this on your own device and know the files you will be accessing you can use the PhoneGap File API: http://docs.phonegap.com/en/2.9.0/cordova_file_file.md.html#File
I know on the forum there are a few examples of how to use it. However, your next hurdle is that you list different file types, so you will have to have some file handling functions, for example, if its a audio file are you going to load it into a player? A video into the video player? PDF, etc.
If you don’t know the files that will be on the device you will need to get a list of them. There are lots of examples online how to do this like:
http://geekyfry.com/html5-tech-it/reading-writing-files-from-sd-card-phonegaphtml5javascript/
That one looks like it passes the files into a div element. To actually do something with the list you will probably want to pass them into an array that you can access, not just look at.
By passing them into an array you can read the extension and then handle that file type.
So, you can see why there really is no easy answer, at least not something you can say heres the file, open it.
I know this probably isn’t the information you were hoping for. My advice to start breaking it down into smaller tasks. Planning your app really well can help solve a lot of these as well.