Which of the following are true regarding encrypted fields?

Answer options:

A.Displayed as mask unless user has view encrypted system permission on profile
B.Will always display encrypted in email templates
C.Existing custom fields can be converted into encrypted fields
D.Encrypted fields can be converted to another field type

Correct Answer: A & B 
Encrypted fields will always displayed as mask unless the user has the permission on his profile to view encrypted system permission. Encrypted fields are used in email templates, but the value will always be masked. 
Option C is incorrect because existing custom fields cannot be converted to encrypted fields 
Option D is incorrect because encrypted fields cannot be converted to another field type. 

https://help.salesforce.com/articleView?id=fields_about_encrypted_fields.htm&type=5