I'm using live forms for users to request a certificate. The users must provide 2 files with personal data. I can send them by email but after that I must delete the files, so that they are not acessible by URL.

How can this be done?

It is not possible at this time. Thanks for suggesting this feature. Please add this to our Community Ideas

We cannot estimate when your feature request will be available; but, we periodically review the list and add new features to the product roadmap.

We would recommend joining the mailing list on our Company News page so you're updated when a new update is released. 

An immediate hotfix might be available under our Premium Support if you're willing to sponsor the development.

 Regarding directory type, in here https://www.mandeeps.com/support/knowledgebase/live-forms-design-form-collect-files it is said that the default directory of the form can be Cloud Storage type, indeed it can be and the files are stored there, but then they are not sent as email attachements. How can I sent them by email with this directory type?

Please follow the below documentation link to send uploaded file as attachment. 

See https://www.mandeeps.com/support/knowledgebase/live-forms-actions-on-form-submission-send-uploaded-file-in-email-as-attachment