foreach (KeyValuePair<int, string> kvp in myDictionary) {...}

 Dictionary<string, string> openWith =

          new Dictionary<string, string>();

            openWith.Add("txt", "notepad.exe");

            openWith.Add("bmp", "paint.exe");

            openWith.Add("dib", "paint.exe");

            openWith.Add("rtf", "wordpad.exe");

Console.WriteLine( openWith["txt"]);