How to add new text into a previously added page using SynPdf

Question

I'm generating a PDF file using SynPdf library in Delphi 10.3.3. I create a lot of pages, after everything finished, I need to write something into the first page (before saving to a file). How can I do this?

Here is my code:

procedure TForm1.Button1Click(Sender: TObject);
var
  lPdf   : TPdfDocumentGDI;
  MyPages: array of TPdfPage;
begin
  lPdf := TPdfDocumentGDI.Create;
  try
    lPdf.VCLCanvas.Brush.Style:=bsClear;
    lPdf.VCLCanvas.Font:=Form1.Font;

    setlength(MyPages,3);
    MyPages[0]:=lPDF.AddPage;
    lPDF.VCLCanvas.TextOut(50, 100, MyString1);
    MyPages[1]:=lPDF.AddPage;
    lPDF.VCLCanvas.TextOut(50, 100, MyString2);
    MyPages[2]:=lPDF.AddPage;
    lPDF.VCLCanvas.TextOut(50, 100, MyString3);
    
    // TextOut something into the first page here

    lPdf.SaveToFile(MyFileName);
  finally
    lPdf.Free;
  end;
end;