1. procedure TMainForm.FormCreate(Sender: TObject);
var
  a: TIOPDFPaperSize;
begin
  // Fill combobox with available PDF paper sizes
  cmbPaperSize.Clear;
  for a := Low(TIOPDFPaperSize) to iepAuto do
    cmbPaperSize.Items.Add(IEPaperSizeToStr(a));
  // Make "US Letter" the selected one
  cmbPaperSize.ItemIndex := cmbPaperSize.Items.IndexOf(IEPaperSizeToStr(iepLetter));
end;

// Set PDF paper size to user's selection
ImageEnView1.IO.Params.PDF_PaperSize := IEStrToPaperSize(cmbPaperSize.Text);

2. ImageEnView1.IO.Params.GIF_DelayTime := 10; // Set current frame to display for 1/10th of a second