Sometimes documents saved to iCloud Drive may be accidentally deleted or disappear due to a syncing error. Apple added the ability to recover documents to help minimize permanent data loss.
1. Log in to icloud.com with your Apple ID on your iPad or computer
2. Click on the "Account Settings" link
3. Towards the bottom of the Settings area, there's an advanced section where you have options to restore files, as well as contacts, calendars/reminders, and Safari bookmarks:
4. After clicking "Restore Files" a window will appear with a list of restorable files--simply check the box next to the files you wish to restore and click the restore button; the file(s) should be restored/accessible on your device again
Currently files are available for restoration 30 days after they're deleted (or marked as deleted). Files deleted beyond that 30 day window are not recoverable.