Android Download app don't show all files from download folder


I am working on a hybrid mobile application and have a problem with listing downloaded files. I am using File Transfer to download a PDF. After the download is completed I check if the file is their with ES File Explorer and everything is ok. The PDF open without any errors. However when I check with the build in “Download” app on my Nexus, the file is not listed. I also tried to copy and paste or create diffrent files in the Download folder but non was later shown in the Download app. How can I make it show all the files from the download folder? I don’t want to force the user to use a file manager.