When creating a new fillable PDF, click on the blue "Share" button in the top right corner of the screen. You'll first need to select Document recipients. If you'd like to send the document via email to primary guardians, select the checkbox that says "Send email reminder". Click "Next"

The Add message screen will open. Add a message to be sent out with your document and click "Send with message" or click "Send without message".

You can always resend documents if parents have not completed them yet.