Apt spells “emacs core docs” as “emacs-common-non-dfsg”.
On a Linux flavor like Ubuntu or Pop!_os which uses
apt for package management?
Trying to find the built-in documentation so you can read it without going online?
$ sudo apt install emacs-common-non-dfsg
It's a license thing. The GNU Project distributes the core Emacs documentation under the GNU Free Documentation License. Debian decided years ago that the GFDL didn't meet the Debian Free Software Guidelines. It's still available – in the non-free repo – though they gave it a name I'll never remember unless I write it down somewhere.
That decision has rippled down over the years. Even though I haven't used Debian since the early 2000's, I needed to know it today. Okay I didn't need to know it. I could have just read the online docs.
I always liked the Info reader and consider it a significant feature when going through an Emacs phase. Though yeah – it's a bit archaic. Honestly that describes most of Emacs. When I want featureful and flashy I can use Visual Studio Code or Atom.
Not even a two hundred word post and I managed to digress. Ah well. Some days are like that.