addWatermark method
Implementation
Future<bool> addWatermark(String text, {double fontSize = 48, Color color = const Color(0x33000000), double rotation = 45}) async {
attach();
final UPdfEdit? edit = _edit;
if (edit == null) return false;
await edit.addTextWatermark(text, fontSize: fontSize, color: color, rotation: rotation);
viewer.invalidateAll();
notifyListeners();
return true;
}