How to create a counter ....

Second link gives you a full example to examine:

import flash.net.*; 
import flash.events.*; 
var textArea:TextField = new TextField(); 
addChild(textArea); 
var PATH:String = "yourFileHere.txt";
var urlRequest:URLRequest = new URLRequest(PATH);
var urlLoader:URLLoader = new URLLoader();
urlLoader.dataFormat = URLLoaderDataFormat.TEXT;
urlLoader.addEventListener(Event.COMPLETE, urlLoader_complete);
urlLoader.load(urlRequest);
function urlLoader_complete(evt:Event):void {
    textArea.text = urlLoader.data;
}

Just change yourFileHere.txt to the right path/file.

Sometimes it's useful to keep the counter in a variable format for url prepending and such but it's not required. Regardless you can find plenty of old tutorials on loading text from a file.

The URLLoader class otherwise can load plain text as well of course.