Автор: http://www.swissdelphicenter.ch

uses
  ComObj;

procedure TForm1.Button1Click(Sender: TObject);
var
  WordApp: OLEvariant;
begin
  Screen.Cursor := crHourglass;
  try
    // Create Word Instance
    WordApp := CreateOleObject('Word.Application');
  except
    ShowMessage('Cannot start MS Word.');
    Screen.Cursor := crDefault;
    Exit;
  end;

  try
    // Open a Word Document
    WordApp.Documents.Add(Template := 'C:\TestDoc.doc');

    // Show Word
    WordApp.Visible := True;

    // Check if FormField exists and asign your text
    if WordApp.ActiveDocument.Bookmarks.Exists('YourFormFieldName') then
      WordApp.ActiveDocument.FormFields.Item('YourFormFieldName').Result :=
        'Your Text';
  finally
    WordApp := Unassigned;
    Screen.Cursor := crDefault;
  end;
end;