The simplest way would be to convert your hexadecimal string to a byte array and use the File.WriteAllBytes
method.
Using the StringToByteArray()
method from this question, you'd do something like this:
string hexString = "0CFE9E69271557822FE715A8B3E564BE";
File.WriteAllBytes("output.dat", StringToByteArray(hexString));
The StringToByteArray
method is included below:
public static byte[] StringToByteArray(string hex) {
return Enumerable.Range(0, hex.Length)
.Where(x => x % 2 == 0)
.Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
.ToArray();
}