How do I read an encrypted completed survey? and can I download a readable version?

When the form is encrypted, you'll be prompted to download the encryption key in order to view the encrypted form responses. If the key is lost, unfortunately, it is not possible to view the submissions. Please refer to the guide below that can help you with more information on form encryption.

https://www.jotform.com/help/344-Encrypted-Forms-and-How-to-Use-Them

Also, it is not possible to download the encrypted form responses since it is required to supply the private key to decrypt the submissions.

Hope this information helps!