As Elastic says in this documentation,
By default, when you install Elasticsearch, Kibana, and Logstash, X-Pack is installed. Starting with version 6.3, X-Pack ships with the default distributions of Elasticsearch, Kibana, Beats, and Logstash. However, X-Pack is under Elastic license, so we are not able to ship this. Instead, we use the OSS distribution.
Also, as you can see here, The installation instructions are only valid for versions 6.2 and older. In versions 6.3 and later, X-Pack is included with the default distributions of Elastic Stack, with all free features enabled by default.
I hope you find this information useful.