I don't know what exactly you want to do with the pen input, but you could use native messaging[0] to get the data into chrome. Basically a small, native program that (bidirectionally) communicates with a Chrome extension via JSON.
I used the same approach to get customer signatures from a Wacom signature tablet into a web app.
I used the same approach to get customer signatures from a Wacom signature tablet into a web app.
0: https://developer.chrome.com/extensions/messaging#native-mes...