This feature is already built in, as far as I can tell...I mean when I'm in a note taking app (any of them) or an office app, and I use the SPen instead of the keyboard, it opens a beige writing bar thing to write on. When I write, it converts that to text. Works like a charm...I take notes this way in SNote all the time.
Samsung Galaxy Note Pro 12.2 Gatsrom Debloated
HTC One X Team Venom ViperXL