As reported in https://bugzilla.redhat.com/show_bug.cgi?id=1329804, the "xdg-open" command checks for the existence of enlightenment_open when the Window Manager is Enlightenment, and hands off requests to it. The user passed a PDF filename to xdg-open, which gets relayed to enlightenment_open, and the result is as follows:
[spot@localhost Documents]$ enlightenment_open calendar.pdf
Filename "file:///home/spot/Documents/calendar.pdf" does not exist or is not a regular file
To be clear, in this example, "calendar.pdf" exists and is a valid PDF file.