Rename the file fundamentals-thirdparty-boopickle-shaded_sjs0.6_2.13-0.10.7-javadoc.jar to fundamentals-thirdparty-boopickle-shaded_sjs0.6_2.13-0.10.7-javadoc.zip
Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder fundamentals-thirdparty-boopickle-shaded_sjs0.6_2.13-0.10.7-javadoc
Double click index.html will open the index page on your default web browser.