function AttachToFile(const AFileName: string; MemoryStream: TMemoryStream): Boolean;
var 
  aStream: TFileStream; 
  iSize: Integer; 
begin 
  Result := False; 
  if not FileExists(AFileName) then 
    Exit; 
  try 
    aStream := TFileStream.Create(AFileName, fmOpenWrite or fmShareDenyWrite); 
    MemoryStream.Seek(0, soFromBeginning); 
    // seek to end of File 
    // ans Ende der Datei Seeken 
    aStream.Seek(0, soFromEnd); 
    // copy data from MemoryStream 
    // Daten vom MemoryStream kopieren 
    aStream.CopyFrom(MemoryStream, 0); 
    // save Stream-Size 
    // die Streamgro?e speichern 
    iSize := MemoryStream.Size + SizeOf(Integer); 
    aStream.Write(iSize, SizeOf(iSize)); 
  finally 
    aStream.Free; 
  end; 
  Result := True; 
end; 

function LoadFromFile(const AFileName: string; MemoryStream: TMemoryStream): Boolean; 
var 
  aStream: TFileStream; 
  iSize: Integer; 
begin
  Result := False; 
  if not FileExists(AFileName) then 
    Exit; 

  try 
    aStream := TFileStream.Create(AFileName, fmOpenRead or fmShareDenyWrite); 
    // seek to position where Stream-Size is saved 
    // zur Position seeken wo Streamgro?e gespeichert 
    aStream.Seek(-SizeOf(Integer), soFromEnd); 
    aStream.Read(iSize, SizeOf(iSize)); 
    if iSize > aStream.Size then 
    begin 
      aStream.Free; 
      Exit; 
    end; 
    // seek to position where data is saved 
    // zur Position seeken an der die Daten abgelegt sind 
    aStream.Seek(-iSize, soFromEnd); 
    MemoryStream.SetSize(iSize - SizeOf(Integer)); 
    MemoryStream.CopyFrom(aStream, iSize - SizeOf(iSize)); 
    MemoryStream.Seek(0, soFromBeginning); 
  finally 
    aStream.Free; 
  end; 
  Result := True; 
end; 

procedure TForm1.SaveClick(Sender: TObject); 
var 
  aStream: TMemoryStream; 
begin
  aStream := TMemoryStream.Create; 
  Memo1.Lines.SaveToStream(aStream); 
  AttachToFile('Test.exe', aStream); 
  aStream.Free; 
end; 

procedure TForm1.LoadClick(Sender: TObject); 
var 
  aStream: TMemoryStream; 
begin 
  aStream := TMemoryStream.Create; 
  LoadFromFile('Test.exe', aStream); 
  Memo1.Lines.LoadFromStream(aStream); 
  aStream.Free; 
end; 

{ 

Note: 

You can't proof whether additional data is attached or not. 
To reach this, you would have to create a checksumm of the 
MemoryStream and attach it.

}