That step isn't as straightforward as you might think.
Put yourself in the shoes of a complete novice. As of this writing, a Google search for {pgp email windows} returns gpg4win as the top search result, which is the tool the author used.
Otherwise, the software listed on the openpgp website (https://www.openpgp.org/software/) mostly doesn't have PGP capability "built in." In particular, both Evolution and Outlook require addons for PGP support.
Despite suffering from bad UX, the instructions the author followed are largely those present in a top-Google-searched guide (https://yanhan.github.io/posts/2017-09-27-how-to-use-gpg-to-... -- infobox result for {gpg encrypted email}). Easier methods that are harder to find or less obvious may as well not exist for a novice such as the author of this article.