Building on Constantin's answer, here's the essence of what I learned while transitioning to Notepad++ as my primary HTML editor.
Install Notepad++ 32-bit
There's no 64-bit version of Tidy2 and some other popular plugins. The 32-bit version of NPP has few practical downsides, so axe the 64-bit version.
Install the Plugin Manager
Plugin Manager isn't strictly necessary for plugin usage. It does make things much easier, though.
Plugin Manager was eliminated from the core package apparently because the developer didn't like some included attribution linking.
You may notice that Plugin Manager plugin has been removed from the official distribution. The reason is Plugin Manager contains the advertising in its dialog. I hate Ads in applications, and I ensure you that there was no, and there will never be Ads in Notepad++.
It's a manual install, but it's not difficult.
C:\Program Files (x86)\Notepad++
. Now you'll see a new entry under Plugins for Plugin Manager.
Install Tidy2 (or your preferred alternative)
In Plugin Manager, check the box for Tidy2. Click Install. Restart when prompted.
To use Tidy2, select one of the preconfigured profiles in its Plugins submenu item, or create your own.