Step 1: To enable Data Encryption, go to Security under the Settings tab of your form, and click to add a password under Encrypt Saved Data.
Step 2: Set your password in the box that pops up. The Formstack team can't retrieve this password for you, so be sure to save it in a safe place.
Step 3: To enable PGP email encryption, go to Security under the Settings tab of your form, and click to add a PGP key under Encrypt Notification Emails with PGP. Copy and paste your public PGP key.
For more information on this feature, read this help article.