Hi,
Since this feature is not yet available on Windows 10 Notepad program, we encourage you to submit your issue using the Feedback Hub. You can either vote on an existing submission or submit a new issue. When you submit a feedback item we gather additional details and information about your issue that will help determine what’s causing it and address it. Feedback items regularly receive Microsoft responses on the submissions in the Feedback app so you can see what we are doing about your feedback. Please revisit frequently to see the status of your feedback items.
For more information on Feedback Hub, see our support article and YouTube video.