using System;

public class Program

{

    public static void Main()

    {

        string[] hexStringsToCheck = { "04fc72cf11fa64e6db9c0675ccdae758", "64E6DB9C0675CCDAE758", " ", "32 ", "said", "ad", "a0f25", "-4", "", null };

        foreach (var text in hexStringsToCheck)

        {

            if (IsHex(text))

                Console.WriteLine("Is Hex: '" + text + "' (" + text.Length + " chars)");

            else

            {

                if (text == null)

                    Console.WriteLine("Is *not* Hex: (null)");

                else

                    Console.WriteLine("Is *not* Hex: '" + text + "' (" + text.Length + " chars)");

            }

        }

    }

    public static bool IsHex(string hexString)

    {

        var isHex = false;

        if ((hexString ?? string.Empty).Length == 0)

            return false;

        if (hexString.Length > 0 && hexString.Length <= 32)

        {

            hexString = hexString.PadLeft(32, '0');

            Guid guid;

            isHex = Guid.TryParse(hexString, out guid);

        }

        else

        {

            throw new NotImplementedException("Use some other way to check the hex string!");

        }

        return isHex;

    }

}