For MS Surface Pro 2 and Win 8.1 Pro there are a few 3rd Party Solutions on the market.
Because Surface Pro 2 contains the WACOM digitzer, you have to install the WACOM driver for 3-dimensional capturing (X,Y position and pressure of the stylus / pen)
If the WACOM driver is installed you can check for the 3rd Party Acrobat / Adobe Reader plugins
SignDoc by SoftPro
SigPDF by Signature Perfect