Rename the file org.kevoree.modeling.microframework.datastores.mapdb-3.5.12-javadoc.jar to org.kevoree.modeling.microframework.datastores.mapdb-3.5.12-javadoc.zip
Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder org.kevoree.modeling.microframework.datastores.mapdb-3.5.12-javadoc
Double click index.html will open the index page on your default web browser.