The Adobe AIR runtime allows you to run AIR applications on the desktop. There are a number of ways to install the runtime. You can install it separately (described below) or it can be installed either when you download and run a sample AIR application or set up your AIR development environment. The runtime only needs to be installed once per computer.. ...

Aside from all the files and other assets that make up your Adobe AIR applications, an AIR application requires an application descriptor, an XML file which defines the basic properties of the application.

When you use Flex Builder 3, the application descriptor file is automatically generated when you create a new AIR project. If you're developing AIR applications using the Flex 3 or AIR SDKs, you must create this file manually. A sample descriptor file, descriptor-sample.xml, can be found in the samples directory of your SDK installation.

Adobe AIR provides classes that you can use to access, create, and manage both files and folders. These classes, contained in the flash.filesystem package, are used as follows:

File A File object represents a path to a file or directory. You use a file object to create a pointer to a file or folder, initiating interaction with the file or folder.

FileMode The FileMode class defines string constants used in the fileMode parameter of the open() and openAsync() methods of the FileStream class. The fileMode parameter of these methods determines the capabilities available to the FileStream object once the file is opened, which include writing, reading, appending, and updating.
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Source: docs.brajeshwar.com