To define viewing permissions, you can add users under "Limit" and they will need to confirm their emails to view the file, preventing them from freely sharing the link. The "Allow All" option allows anyone to view the files, but they will need to enter their name and email to create a person in your directory. The other two options only require an email corresponding to the user's email you've invited. Changing permissions does not automatically send emails, but you can achieve this by giving permission to contacts in a pipeline stage and adding an email template with the link to the data room.