procedure TForm1.btn2Click(Sender: TObject);
var
  doc : IHTMLDocument2;
  col : IHTMLElementCollection;
  el : IHTMLElement;
  i : integer;
begin
doc := wb1.Document as IHTMLDocument2;
 col := doc.all.tags('textarea') as IHTMLElementCollection;
  for i := 0 to col.length-1 do
  begin
    el := col.item(i, 0) as IHTMLElement;
    el.setAttribute('value', 'Marsel', 0);
  end;
end;

procedure TForm1.btn2Click(Sender: TObject);
var
  doc : IHTMLDocument2;
  col : IHTMLElementCollection;
  el : IHTMLElement;
  i : integer;
begin
doc := wb1.Document as IHTMLDocument2;
col := doc.all.tags('input') as IHTMLElementCollection;
for i := 0 to col.length-1 do
  begin
    el := col.item(i, 0) as IHTMLElement;
    if el.getAttribute('type', 0) = 'file' then
      el.setAttribute('value', 'Marsel', 0);
  end;
end;