On an online exam, the teacher likes to receive the students' submissions (pdf document) anonymously without knowing their emails and names. In that case, I tried making a Google form that will receive only the exam roll and registration number from the students. But when I add a File Upload option, the form starts asking to sign up and consequently collecting the students' names associated with the Gmail accounts!
So, what are the most effective and easy-to-use online tools/platforms to receive the students' submissions anonymously? Note that self-hosting type things are not preferable, and I'm looking for free service. The platform may collect data, but the receiver should not find out the senders name and email.
(It was asked on Web Applications. But it's off-topic and closed there.)