string hexstring = "396c6976657373";
byte[] letters=new byte[hexstring.Length/2];
ASCIIEncoding encoder = new ASCIIEncoding();
for (int i = 0; i < (hexstring.Length-1); i += 2) {
letters[i/2]=Convert.ToByte(hexstring.Substring(i,2),16);
}
string woord = encoder.GetString(letters);