Once you are logged into cloud.acrobat.com, select 'Sent Files' from the left panel
Select the file/parcel you want to stop sharing
Select the Unshare Icon
If you want to then share with individuals simply select the file/parcel and select the Forward icon - this will create a new parcel which you can then share with individuals.
Does this mean that any time I send photos or other files to someone that they are public? That doesn't make sense to me.