Date: 2019may31 OS: Linux, Android Q. Android saying "Can't open file" and not showing Android icon for a downloaded apk A. This worked for me. My server was not setting the Content-Type in the header correctly. I was surprised that Android retained this after the download but it did. For RedHat/Fedora/CentOS add this line to /etc/mime.types

application/vnd.android.package-archive apk

And restart Apache or other webserver