Text Properties "Aa" Grayed Out

I can make a text box, and select my text properties. BUT - if I want to go back and change text properties (font, font size, justification, whatever) I can not access the text properties. The "Aa" icon is grayed out. I can change the text BOX properties, but not the text properties. What gives?

Related question: how do I center text from top to bottom in a text box, vs. from left to right?

(Brand new installation of Adobe Acrobat Reader DC on Windows 10)