Make an area that is only accessible through buying a game addon?

So basically, I am quite new to scripting and I REALLY need some hints and tips here guys.
I want to make an area of my map blocked off, until say… They purchase the addon which unlocks the next area…
How would I go about doing this…
I was thinking if anyone new any codes that would check a directory for a file and if it’s there it will remove the invisible barrier and allow access through the city?
I’m sure this is a much asked question for people who have just started, so please reply fast.

OUTLINE OF WHAT I NEED/IDEA

Help with writing a script that will check the system directory… (eg. C:\Users\Desktop\Addon.dll, Obviously I can encrypt the DLL file so you can’t just make it yourself) and then if that file exists and contains a certain text inside… Then a gameobject that will be blocking the way (or multiple game objects) will then allow access.

CAN ANYONE HELP ME?!

So far I have this for my checking of the file code…

function Start () {

}

function Update () {
	
	if (System.IO.File.Exists("D:\Addon\AddonCheck.txt")) {
	
	//Remove or disable gameObject. THIS IS WHAT I DON'T KNOW HOW TO DO.
	
	}

}

Also this only checks if the file exists, not if the file has a certain string in it. I need it to check the file and see if it contains the string of say… “addon 1.1 = true”
And if it says this then it will unlock a certain gameObject allowing the player to walk through…

May I add that the text file will be able to contain different addons if they have more than one… So it should check for all of them…

Thanks!
-Aaron

Here is an example I found on the forums:

http://forum.unity3d.com/threads/99427-Step-by-step-tutorial-for-c-.net-dll-and-Unity3D(Pro-only).

It states there how to load the dll and access functions inside it.

I think that is what you are looking for.

After checking if the file in there, load it, then use some function to make sure this is your real addon file.