Adobe Reader is a handy app for viewing, sharing, and annotating PDF documents. You can post comments with the Add Text tool, and insert "sticky notes" anywhere in the PDF. The freehand drawing feature is useful for marking up documents, as are the highlight, strikethrough, and underline tools. The Galaxy Note's stylus is particularly useful for filling in and signing PDF forms. The free Adobe Reader works with a variety of PDF file types, including password-protected documents.