PDF Encryption

• What is PDF email encryption?
• With PDF encryption, are attachments encrypted as well?
• Is PDF encryption safe? Some companies claim they can crack PDFs?
• With PDF encryption, how can the recipient securely reply ?
• There are different password modes for PDF encryption. Which mode is the most secure?
  • Static password
  • Random password via SMS
  • Random password, sent back to sender
  • One Time Password (OTP) using the online portal
• With the One Time Password (OTP) mode, a recipient can be invited. Is this not insecure? What happens if the invite is intercepted?
• Is HTML email supported by PDF Messenger?