Как сделать чтобы документ сохранялся именно в .txt

__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
  // Initialize the dialog filters to open/save *.txt files
  // and also files with arbitrary extension.
  OpenDialog1->Filter = "Text files (*.txt)|*.TXT|Any file (*.*)|*.*";
  SaveDialog1->Filter = "Text files (*.txt)|*.TXT|Any file (*.*)|*.*";
}

Memo1->Lines->SaveToFile(SaveDialog1->FileName+".txt");

__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
  // Initialize the dialog filters to open/save *.txt files
  // and also files with arbitrary extension.
  OpenDialog1->Filter = "Text files (*.txt)|*.TXT|Any file (*.*)|*.*";
  SaveDialog1->Filter = "Text files (*.txt)|*.TXT|Any file (*.*)|*.*";
}
 
void __fastcall TForm1::Button1Click(TObject *Sender)
{
  // Execute an open file dialog.
  if (OpenDialog1->Execute())
    // First, check if the file exists.
    if (FileExists(OpenDialog1->FileName))
      // If it exists, load the data into the memo box.
      Memo1->Lines->LoadFromFile(OpenDialog1->FileName);
    else
      // Otherwise, throw an exception.
      throw(Exception("File does not exist."));
}
 
void __fastcall TForm1::Button2Click(TObject *Sender)
{
  // Execute a save file dialog.
  if (SaveDialog1->Execute())
    // First, check if the file exists.
    if (FileExists(OpenDialog1->FileName))
      // If it exists, throw an exception.
      throw(Exception("File already exists. Cannot overwrite."));
    else
      // Otherwise, save the memo box lines into the file.
      Memo1->Lines->SaveToFile(SaveDialog1->FileName);
}

void __fastcall TForm1::Button2Click(TObject *Sender)
{
  // Execute a save file dialog.
  if (SaveDialog1->Execute())
    // First, check if the file exists.
    if (FileExists(OpenDialog1->FileName))
      // If it exists, throw an exception.
      throw(Exception("File already exists. Cannot overwrite."));
    else
      // Otherwise, save the memo box lines into the file.
      if (ExtractFileExt(SaveDialog1->FileName).LowerCase() == ".txt")
          Memo1->Lines->SaveToFile(SaveDialog1->FileName);
      else
          Memo1->Lines->SaveToFile(SaveDialog1->FileName + ".txt");
}

    // Execute a save file dialog.
    if (SaveDialog1->Execute())
        // First, check if the file exists.
        if (FileExists(SaveDialog1->FileName)) // Не OpenDialog, а SaveDialog
            // If it exists, throw an exception.
            throw(Exception("File already exists. Cannot overwrite."));
        else
             Memo1->Lines->SaveToFile(ChangeFileExt(SaveDialog1->FileName, ".txt"));