How do I stop PDFs opening as tabs in the same document?

In the past, if I clicked 2 or more pdfs to open them with Adobe Reader DC they opened as separate documents in separate windows and I was happy with that. I have to compare changes to documents frequently in my work and being able to open 2 pdfs side-by-side made that easy.

Now if I open more then one pdf, they open as tabs in the same pdf window. If I want to look at the pdfs side-by-side, I have to drag one of them out of the window onto my desktop and open it separately.

What do I do/what setting do I change to make it go back to the way it was?

Thank you community for your help!