Use the event document-sharing controls to give the right people access to a file.
Share a document
Open the event's Documents area, then upload or choose the document.
Open Share and find the intended event contacts.
Use the checkbox under Can View This Document to add or remove access.
Wait for the change to save, then use Close to leave the dialog.
The checkbox changes access immediately
There is no separate Save or notification choice in this share dialog. Adding a new recipient requests a real document-sharing notification. Delivery depends on the applicable event/email settings; it is not guaranteed merely because access was granted.
Choose recipients carefully
The person must be an appropriate event contact, and you must have permission to change the document. Internal lead files are not automatically shared. Check the file for private notes before giving access. Removing portal access does not recall a copy someone has already downloaded.