You could try using a file stream.
Seek()
to the position you want to start from and then
Read()
the bytes you need.
Edit: You mentioned to need only one byte. The code is updated for that need.
using (System.IO.FileStream stream = new System.IO.FileStream(filepath, System.IO.FileMode.Open))
{
int startIndex = 0xFFF0;
stream.Seek( startIndex);
byte data = stream.ReadByte();
stream.Close();
}
Error handling is left to the implementer, of course.