Use the Calendar app to create and edit events, appointments, and meetings.
Tap the event, then tap Edit.
In the event details, tap Add attachment.
Locate the file you want to attach.
To find the file, you can enter its name in the search field, scroll, tap folders to open them, tap Browse to look in other locations (such as iCloud Drive), and so on. See at the top of the screen after copying an event.
Tap the copied event below Title.
Tap Add.
You can change the time of an event and any of the other event details.
Go to the Calendar app Send invitations in Calendar on iPad