Hello MichaelKim8,
Thanks for posting your concern here.
Surface Pen actually works on variety of Surface devices running in Windows 10. If your device is touchscreen enabled, you will be able to draw or write on limited application such OneNote, Whiteboard, and etc. On the other hand, if your device is not touchscreen enabled, then the Surface Pen can act as a mouse-alternative, with buttons for left and right-clicking helps you to select and drag items. See How to use your Surface Pen for more details.
You can actually upgrade your Windows 10 Home to Pro without worrying your files as the upgrade will not affect your files and apps. For OneNote, it only attaches a copy of the source document or file. OneNote does not maintain a link to the source file.
If this answers your question, please let our Community know by marking this post as an answer. Otherwise, don't hesitate to respond to this thread if there’s anything else that needs to be addressed.
Kind regards,
StevenK