public var file:FileReference = new FileReference();

public function doLoad( event:Event ):void
{
	file.addEventListener( Event.SELECT, doFileSelect );
	file.addEventListener( Event.COMPLETE, doFileComplete );
	file.browse( [new FileFilter( "Text File", "*.txt" )] );
}

public function doFileSelect( event:Event ):void
{
	file.load();
}

public function doFileComplete( event:Event ):void
{
        // txtField is the instance name of a text field used to display loaded content.
	txtField.text = file.data.readMultiByte( file.data.bytesAvailable, "utf-8" );
}

Adobe AIR - Load local text file

file, actionscript, text

ActionScript 3