Currently Blender on Windows does not appear to support Stylus hardware without the need for the WinTab driver, for example the stylus functionality does not work on a Microsoft Surface Book and pen without the WinTab driver being installed. Windows 8 added support for stylus hardware but including the WM_POINTERUPDATE Windows message, GetPointerInfo and GetPointerPenInfo API.
This pull request provides native support for these stylus devices without needing the WinTab driver, it should also resolve this bug report for Microsoft Surface Book 2 see https://developer.blender.org/T57869.
This is my first Blender request. It needs some definitions (copied from WinUser.h) for the WM_POINTERUPDATE message, as well as the GetPointerInfo and GetPointerPenInfo API. I tried to follow the existing methods but any advice would be useful. I tested it using the Grease Pencil and tested using the pointer and eraser on a Microsoft Surface Book 1.