This is available via Office 365 and G-Suite enterprise level services so no it's not aimed at individual level usage. Both are whole encrypted email solutions and are quite simple to implement and use without using UI we as end-users are not familiar with.
The recipient gets an email telling them they have a secure email. They click the link and follow instructions to get to view the email like Proton & Tutanota.
Most people here would not take on the cost to implement any option without specific requirement. I worked for MS supporting O365 product lines for 3 years directly, by training other technicians, & later by providing O365 & GSuite deployments to enterprise clients under my own banner. IE... I know how they work & what I state is accurate.
Laws would need to be written to force title, lending, etc to use encrypted email to protect client data. And if that were the case; those encrypted emails will be initiated from the corporate end in our line of work. That communication will also provide an avenue to provide an encrypted response using the same platform.
This effectively negates individual notary's need to invest in even a free solution like PGP let alone a subscription based one.
PGP has it's flaws. The article was too simple in its direction of implementing it. A set of subkeys should be used. If one of the keys is compromised, you only need to revoke it and regenerate a new one. This negates the need to revoke the master key, the one that holds your digital identity. This strategy offers a much higher level of security.
All of it is moot anyway if your PC is compromised and you are the typical end-user who selects the easier way of utilizing the tools no matter the option used.
And just like PDFs... Microsoft formatted docs can ALL be unlocked with readily available tools. They are not secure. Most any password protected MS Office document can be opened in a matter of seconds to minutes.