Mac Preview: how do I discplay the sidebar
Hi, I'm looking at a PDF file. The sidebar was hidden, so I wanted to show it. When I look at the View menu, "Hide Sidebar" is checked. When I select "Hide Sidebar" in the View menu to un-check it, the Sidebar does not appear; the menu item remains checked. Re-starting Preview does not fix this. Re-booting the computer does not fix this. This is repeatable in multiple PDF files. The sidebar goes away and never comes back. There's no user manual for Preview that I can find. Search through questions was fruitless. So posting here. Mac Pro Tower 2010 running Mac OS 10.12.6. Thanks.
Mac Pro, macOS Sierra (10.12.6)