Please follow the steps listed below to get this use case working on your local AEM instance.
Deploy the DevelopingWithServiceUser Bundle contained in the zip file.
Add the following entry in the Apache Sling Service User Mapper Service DevelopingWithServiceUser.core:getformsresourceresolver=fd-service using the configMgr.
Deploy the newsletters bundle. This bundle contains the code to list the folder contents and assemble the selected newsletter(s).
Import the package using Package Manager. This package contains client library and sample pdf files to test the solution.
Import the sample adaptive form. This form will list the newsletters that can be selected.
Preview the form.
Select a couple of newsletters to download.The selected newsletters will be combined into one pdf and returned to you.