[AlexSku]

Код:

procedure TForm1.Button1Click(Sender: TObject);
begin
  if OpenDialog1.Execute then
    with Memo1 do
    begin
      Lines.Clear;
      Lines.LoadFromFile(OpenDialog1.FileName);
      SetFocus;
      SelStart:= Length(Lines.Text) ;
      SelLength:= 0;
    end;
end;