Rename the file powsybl-single-line-diagram-cgmes-iidm-extensions-3.3.2-javadoc.jar to powsybl-single-line-diagram-cgmes-iidm-extensions-3.3.2-javadoc.zip
Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder powsybl-single-line-diagram-cgmes-iidm-extensions-3.3.2-javadoc
Double click index.html will open the index page on your default web browser.
