Edit shared iWork files in iCloud Drive on iCloud.com
In iCloud Drive on iCloud.com, do one of the following:
If you’re the owner: Double-click the file.
If you accepted the invitation to the shared file: Double-click the file.
If you’ve been invited to edit a file, but haven’t accepted the invitation: Click the link you received, then click Add to iCloud Drive or Open in [iWork app].
After you open the file for the first time, it appears in iCloud Drive.
Edit the file.
When someone edits a shared iWork file, everyone sharing the file sees the changes, but no one can see who made them. The timestamp below the file in iCloud Drive shows the last time it was edited.
If you’re invited using an email address or phone number that isn’t associated with your Apple ID, you need to follow the onscreen instructions to associate it before you can add the file to iCloud Drive.