Can't Keep Multiple PDF's Open in Adobe Reader Touch

Hi, 

I don't know if this is some weird default setting, or a weird glitch. I'm coming from Mac to PC and completely baffled. Hope someone can help!

I can open a PDF and view it, no problem. The problem is that when I open a second PDF, the first one closes. It appears that I cannot have two PDF's open at the same time. Not in different windows, not in different tabs. Just one PDF at a time, full stop. 

I'm using Adobe Reader Touch v3.1, Build 87675 on Windows 10 Home v21H1. 

Any ideas? Is this a product "feature", setting or glitch?

Thanks!