No, though depending on what you do, win32.hlp is still valid (you'll need to replace the Win10 winhelp stub with a real version from an earlier version of Windows though since Microsoft hasn't released a Win10 version of winhelp).
However your best best is to find some MSDN CD/DVD image that still uses CHM and use that. Also note that the Win32 documentation apparently went through a ton of conversions and in the process some entries were lost (in that the API docs are there but the docs are missing parts).
The official docs site has PDFs for download but those are automatically generated from the section you are reading and they have cutoff points that feel arbitrary (so you can't go to the highest section for Windows and download all docs). You can find a PDF for the Win32 API reference for handling windows[0] but it contains only the reference and you need to go to another place for the guide (in comparison the win32.hlp and MSDN documentation had both).
These PDFs are also awful, they look like printed websites, they have zero grouping (the sidebar bookmarks are per header file) and the bookmarks are even broken (clicking on one will move you +/- 1 page off).
The "source code" for the docs is apparently on GitHub[1] but it looks like a conversion to markdown and not the real source. Though theoretically it could be possible to parse it and create a proper CHM (or whatever) file out of it since the docs are there [2]. Sadly it only includes the reference and not the guides (but they might be somewhere else on that GitHub account, there are 2300+ repositories, so good luck finding it :-P).
However your best best is to find some MSDN CD/DVD image that still uses CHM and use that. Also note that the Win32 documentation apparently went through a ton of conversions and in the process some entries were lost (in that the API docs are there but the docs are missing parts).
The official docs site has PDFs for download but those are automatically generated from the section you are reading and they have cutoff points that feel arbitrary (so you can't go to the highest section for Windows and download all docs). You can find a PDF for the Win32 API reference for handling windows[0] but it contains only the reference and you need to go to another place for the guide (in comparison the win32.hlp and MSDN documentation had both).
These PDFs are also awful, they look like printed websites, they have zero grouping (the sidebar bookmarks are per header file) and the bookmarks are even broken (clicking on one will move you +/- 1 page off).
The "source code" for the docs is apparently on GitHub[1] but it looks like a conversion to markdown and not the real source. Though theoretically it could be possible to parse it and create a proper CHM (or whatever) file out of it since the docs are there [2]. Sadly it only includes the reference and not the guides (but they might be somewhere else on that GitHub account, there are 2300+ repositories, so good luck finding it :-P).
[0] https://docs.microsoft.com/en-us/windows/win32/api/_winmsg/
[1] https://github.com/MicrosoftDocs/sdk-api/
[2] https://github.com/MicrosoftDocs/sdk-api/blob/docs/sdk-api-s...