The official documentation for using other libraries in Web AppBuilder points to libs/main for including AMD modules in multiple widgets. I want to use Proj4js in my widgets, so I deployed it in the d:\WAB\client\stmapp\libs directory and added the path ("./proj4js/dist/proj4") into the libs/main.js dependency array. The path to the proj4.js file is d:\WAB\client\stmapp\libs\Proj4js\dist\proj4.js, which should be where the setting is pointing to. This should be enough according to the documentation, but it doesn't work. <A class="jive-link-external-small" href="https://community.esri.com/external-link.jspa?url=http%3A%2F%2Fmyname%2Fwebappviewer%2F%3Fconfig%3Dsample-configs%2Fconfig-demo.json" target="_blank">http://myname/webappviewer/?config=sample-configs/config-demo.json</A>