Conversion of hexadecimal string to string
I don't think there is a built-in method. Yours is pretty good but we could make some improvements:


Parameters should be camelCase => hexString.
You should favour StringBuilder when building up strings.
You should step through the string in increments of 2 to cut down on the maths.
You should validate the argument.
You should prefer var when the type is obvious.


Result of those points:

string HexStringToString(string hexString) 
{
    if (hexString == null || (hexString.Length &amp; 1) == 1) 
    {
        throw new ArgumentException();
    }
    var sb = new StringBuilder();
    for (var i = 0; i &lt; hexString.Length; i += 2) {
        var hexChar = hexString.Substring(i, 2);
        sb.Append((char)Convert.ToByte(hexChar, 16));
    }
    return sb.ToString();
}