Added a PDF to the Root\media\com_eventbooking folder. It did not show up in the event configuration edit page in the basic information tabs Attachment Pulldown.
I tried to remove it and then add it again.
This did work at one point but I had to change the document and that broke it.
That's strange. Maybe the file you uploaded is not available in "Attachment File Types" config option in Events Booking ? Could you please check and make sure the file type has been added to Attachment File Types config option of EB ?