Can you clarify what you're looking for? The ability to convert
handwriting t text is built into the product and there's no separate
download or plug-in required. This assumes that you have a version of
Windows that supports the Ink interface (typically Tablet PCs will have
this preloaded). If you have a different type of hardware that supposedly
works with OneNote, it should include whatever drivers are needed to make
OneNote accept the input and treat it as Ink.
Is that "sent via smart pen device" from a menu in a piece of software?
Can you give some more details on your hardware and software configuration?