IIRC Notepad source code is in a Windows SDK. Probably an old one, but it only started to be actively maintained quite recently (and even then: only very lightly), so the source code you can get will likely cover most of its lifespan for now.
I'm not sure the source of notepad is that much interesting, though. I mean, yeah, nice to have out of curiosity, maybe, but I'm not sure I would get anything from looking at it. I'm even more interested by monstrosities like historical version of conhost, or of cmd, because it is both simultaneously horrendous and bizarrely not extremely buggy (probably was debugged by some kind of brute force effort, then... :p )
Although a version of the Notepad source under a free software licence would at least permit to strip it of the new ridiculous shits, like "Search with Bing" and maybe some spying features.
I'm not sure the source of notepad is that much interesting, though. I mean, yeah, nice to have out of curiosity, maybe, but I'm not sure I would get anything from looking at it. I'm even more interested by monstrosities like historical version of conhost, or of cmd, because it is both simultaneously horrendous and bizarrely not extremely buggy (probably was debugged by some kind of brute force effort, then... :p )
Although a version of the Notepad source under a free software licence would at least permit to strip it of the new ridiculous shits, like "Search with Bing" and maybe some spying features.