If configured by the meeting administrator, (via the Meeting Type Participant Site Settings Allow Custom Documents) participants can upload their own attachments to an individual agenda item by selecting Browse and Upload from the item details on the right hand side of the page. 

The attachments are uploaded as private files by default.  The participant has the option of making the attachment Public by selecting the Make Public check box from the drop down. In this case the attachment will be view-able by all meeting participants. If Public option is not selected, then only the participant who uploaded the document will be able to see it.

Related Articles:

1. Web Portal - Adding Comments
2. Participant Web Portal - Voting
3. Web Portal – Current Item Link
4. Web Portal - Clearing Private Comments
5. Web Portal - Requesting to Speak
6. Web Portal - Pinning Meeting Sites
7. Web Portal – Pinning Agenda Items
8. Web Portal - Downloading Agenda Package for Offline Use