procedure TForm1.FormCreate(Sender: TObject);
var MyFile:file of byte; a,b:byte;
begin
  AssignFile(MyFile, 'C:\Test.txt');
  ReWrite(myFile);
  a:=66;
  b:=67;
  write(myfile,a);
  write(myfile,b);
  CloseFile(myFile);

  FileMode := fmOpenRead;
  Reset(myFile);

  while not Eof(myFile) do
  begin
    Read(myFile, a);
    ShowMessage(IntToStr(a));
  end;

  CloseFile(myFile);
end;