Rename the file hawtio-example-springboot-authentication-jar-3.0-beta-1-javadoc.jar to hawtio-example-springboot-authentication-jar-3.0-beta-1-javadoc.zip
Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder hawtio-example-springboot-authentication-jar-3.0-beta-1-javadoc
Double click index.html will open the index page on your default web browser.