Read hex in C# using IO

Don't use a StreamReader—that's only for characters in a certain encoding (default UTF8). Use a FileStream class instead:

FileStream fs = new FileStream(fileDirectory, FileMode.Open);
int hexIn;
String hex;

for (int i = 0; (hexIn = fs.ReadByte()) != -1; i++){
    hex = string.Format("{0:X2}", hexIn);
}