Is submitting an extended PDF form secure?

I have created loan application for a client and saved it as an extended PDF that is fillable, savable, and has Submit button to send the completed application via email to the client's loan department. The client will send the form back to the applicant for a signature (via RightSignature, the service the client uses). The question is whether the information in the submitted form is at risk (not secure) when the form is submitted via the email (when the applicant clicks the Submit button).