Also, it's not just (allegedly) all of XP source that's been leaked:
https://www.bleepingcomputer.com/news/microsoft/the-windows-...
It's also Windows Server 2003, MS DOS 3.30, MS DOS 6.0, Windows 2000, Windows CE 3, Windows CE 4, Windows CE 5, Windows Embedded 7, Windows Embedded CE, Windows NT 3.5, and Windows NT 4!
That's a huge amount of stuff to analyse.
As a recall, making notepad is like a homework assignment for a visual basic class. You just drag the text editor window and add the menus, there isn't a whole lot there!
Paint would probably be a bit more work, but there are a few clones out there already
What GP meant, is whether the source for those controls is available.
[1]: https://docs.microsoft.com/en-us/windows/win32/controls/indi...
The same goes for Mac. Mac has "textEdit" and "Notes" apps but it handles formatting, is slower to launch and is more of a Wordpad clone. For Paint, their Preview tool is terrible. I just want to take a screenshot, paste it in a file, maybe add a red circle or square and save it as png. Quick and fast.