Secure Delivery is at Security > Security. Its dialog box offers four steps to protect files you plan to distribute.
Select envelope
Opens the Envelope Panel so you can choose an envelope to contain and protect a set of attached files
Add Attachments
Browse for the desired files; PDF and other file types are accepted.
Encrypt Files
Open the Security panel. Choose a security scheme to encrypt the attachments or the envelope with Password Security or Certificate Security.
Sign Document
Opens the Sign/Certify panel. Choose a signature scheme for the envelope, or place a signature without using a scheme.
When ready, click Send. Your default mail application opens with a new message including the file set in an envelope.