best response confirmed by Paul_VC (Contributor)
Solution

@Paul_VC 

 

I wanted the same thing, not needing additional software for the pdf preview in outlook.

Wanting to use edge. However this seems not possible.

I've now found out that when you install Microsoft Power Toys you get a number of cool tools, including a pdf previewer that works in outlook.  It is additional software, but at least you don't have to install a separate pdf viewer.