Rename the file com.liferay.layout.type.controller.control.panel-6.0.14-javadoc.jar to com.liferay.layout.type.controller.control.panel-6.0.14-javadoc.zip
Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder com.liferay.layout.type.controller.control.panel-6.0.14-javadoc
Double click index.html will open the index page on your default web browser.