I had this stroke of insight while watching my mother trying to open a pdf from outlook.com

Firstly, what percentage of the population knows (or cares) what PDF even means? All they want is to read whats attached and do what they need to without "downloading" something, finding it on their own computer somewhere and then finding out, after much stress that they need something called "adobe".

This way you could take every single step out of the process :)