Use a TMemoryStream to read the file, then use the TMemo's SetSelTextBuf() method to insert the text;

var
  TheMStream : TMemoryStream;
  Zero : char;
begin
  TheMStream := TMemoryStream.Create;
  TheMStream.LoadFromFile('C:\AUTOEXEC.BAT');
  TheMStream.Seek(0, soFromEnd);
//Null terminate the buffer!
  Zero := #0;
  TheMStream.Write(Zero,  );
  TheMStream.Seek(0, soFromBeginning);
  Memo .SetSelTextBuf(TheMStream.Memory);
  TheMStream.Free;
end;