var
  FAbort: Boolean;

procedure TForm1.FormCreate(Sender: TObject);
begin
  FAbort := False;
end;

procedure TForm1.btn1Click(Sender: TObject);
begin
  if dlgOpen1.Execute then
    edt1.Text := MD5Print(MD5File(dlgOpen1.FileName, MD5CalcPrgssProc)));
end;

procedure TForm1.MD5CalcPrgssProc(ATotal, AProgress: Int64;
  var Cancel: Boolean);
begin
  pb1.Position := Round(AProgress / ATotal * 100);
  Cancel := FAbort;
end;