How to compare between two executable files?

I have a file which doesn't require UAC Warning. I copied the file to another location using C#.NET

 File.Copy("Original.exe", "Copy.exe");

Now i see that Copy.exe require UAC warning to run under windows 7/Vista.

How can i compare between Original.exe and Copy.exe to see exactly what happened to the file and change it manually so that it doesn't require UAC anymore. Which tool can i use to achieve that ?

BOTH EXECUTABLE ARE THE SAME FILE : How to know the difference between these two files ?