Rename the file integration-tests-data-index-service-quarkus-1.43.0.Final-javadoc.jar to integration-tests-data-index-service-quarkus-1.43.0.Final-javadoc.zip
Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder integration-tests-data-index-service-quarkus-1.43.0.Final-javadoc
Double click index.html will open the index page on your default web browser.