procedure Tform1.Step;
var
  i: Integer;
begin
   ProgressBar1.StepIt;
   Sleep(12);
   ProgressBar1.StepBy(12);
   ProgressBar1.Max:=100;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  i: Integer;
begin
  if OpenDialog1.Execute then
  begin
    if FileExists(OpenDialog1.FileName) then
    begin
      Step;
      Memo1.Lines.LoadFromFile(OpenDialog1.FileName);
      ProgressBar1.Position:=0;
    end;
  end;
 end;