Прочитать и изменить текстовый файл строка за строкой

Оформил: DeeCo

procedure TForm1.Button1Click(Sender: TObject);
 var
   i, z: Integer;
   f: TextFile;
   t: string;
   Data: array of string;
 begin
   if OpenDialog1.Execute then
   begin
     //Read line by line in to the array data 
    AssignFile(f, OpenDialog1.FileName);
     Reset(f);
     z := 0;
     SetLength(Data, 0);
     //Repeat for each line until end of file 
    repeat
       Inc(z);
       readln(f, t);
       SetLength(Data, Length(Data) + Length(t));
       Data[z] := t;
     until EOF(f);

     SetLength(Data, Length(Data) + 3 * z);
     //Add to each line the line number 
    for i := 1 to z do Data[i] := IntToStr(i) + ' ' + Data[i];
     SetLength(Data, Length(Data) + 2);
     //Add a carriage return and line feed 
    Data[1] := Data[1] + #13 + #10;
     i       := Length(Data[5]);
     Data[5] := '';
     SetLength(Data, Length(Data) - i);
     //create a new textfile with the new data 
    AssignFile(f, OpenDialog1.FileName + '2');
     ReWrite(f);
     //write all lines 
    for i := 1 to z do writeln(f, Data[i]);
     //save file and close it 
    CloseFile(f);
   end;
 end;