Not ideal but as a stop-gap, but to those who are desperate for this feature
You could set up Windows task scheduler and powershell to open the mht, “print” to pdf then email.
Takes a bit of effort, trial and error to get it working but it is very much doable.
I had done this in a previous role but was about 4 years ago when I set it up so I would have to figure it out again and as I currently have no need for it, it’s not something I can get into specifics about.
If I have time at some point i’ll try and create a tutorial but it will be some time off in the future.
Also to take some of the heat off of the Gurock crew, custom PDF solutions take a lot of work to integrate, and off the shelf solutions can cost big $ in licensing and still come with in a large overhead in integration.