Hi,
Thanks for using The Events Calendar Pro.
Currently, we do not have a feature to upload and attach a file to an event with our additional fields.
You can use a plugin that creates Custom Fields and add one yourself.
Then you could follow the themer’s guide and the documentation from that plugin on how to display on the front end of your site.
https://theeventscalendar.com/support/documentation/events-calendar-themers-guide/
Let me know if you have any follow up questions.
Thanks