All you got to do is to use flash.filesystem.File class. With it, you can open a file with the load() method to open the local file, you can use the save() method to save the content at local machine. Finally, you can use the upload() method to send the file to a server.
Here is a example in Flex, but it's very easy to port to pure AS3: http://www.adobe.com/devnet/air/flex/articles/uploading_air_app_to_server.html.
Any doubt, just post it!
Thanks for that. One thing though (I am pretty new to this so be gentle)...
No problem, friend!