A free program for Android, by Yo Android.

Writing, signing, and drawing on existing PDF files is made significantly simpler with the help of Yo Pdf Writer. Simply pick a PDF file to write on, and you can get started right away. You can easily sign On PDF by using the app’s built-in signature feature. Alternatively, you can also use your finger or stylus to draw on it. Yo Pdf writer also lets you draw lines, highlight text and make a signature on your pdf form conveniently. You even have the ability to rapidly draw lines, highlights, shapes, and signatures onto your PDF files when you use the Draw Tool that comes with Yo Pdf Writer.