I need the ability to write freehand. Can PDFpen work with my tablet device?

Yes, PDFpen works with pen tablet devices such as Wacom Bamboo and Axiotron's Modbook. There is also a version of PDFpen for the iPad (see PDFpen for iPad & iPhone). For quick markups, you can use the "Scribble Tool"  and draw with your trackpad for freehand drawing on your PDF.

To use this tool open your PDF in PDFpen, select the Scribble Tool and write away.