PDF Annotator has an impressively good record if you google it. However, there are disadvantages:
1) Handwritten notes cannot be recognized as text. Thus, they are not searchable.
2) If you enter text notes through the Windows input panel, they will not be completely visible in Acrobat 7.0. Maybe this is caused by my non-standard dpi setting.
3) The handwritten notes look very smooth in PDF Annotator, but they do not in Acrobat 7.0.