For those not using it, I'd recommend it. I had it years ago and forgot it exists, but when Microsoft Photos stopped working on my system I downloaded it again. It opens almost any file type from raster to vector files like EPS, AI, PDF, PS etc. Pretty much instantly. It's a great viewer.
Also, I am not sure if I learned this here or not, but changing the extension from .ai to .pdf will allow ai files to open in acrobat.
