In order to send a file securely, I am going to encrypt/password protect a PDF file with Preview on macOS.
Other question(s), such as this one have asked the method of encryption for PDF's in general, but not about Preview on macOS specifically. I learned from that question that Adobe Acrobat uses very secure encryption methods, but I am unsure how Preview on macOS handles this.
I am on macOS 10.12.6. I am encrypting a PDF by going to File>Export>Encrypt in Preview.app.
This is similar to my other question here.