How do I hide the sidebar when I open a pdf using OS X El Capitan's Preview application?
In the upper left corner right under the red close window button there is an icon that looks like a box with something on it's left side. There is a down arrow next to the box. Click it. From the menu that appears check Hide Sidebar. You can also select Hide Sidebar from the Viewmenu or press OPTION-COMMAND-1 on your keyboard.
How does a user hide or move the thumbnail sidebar in PDF files on iPad?
You can italic double-click a PDF italic or image file italic to open it by default in Preview. ... Close the sidebar italic Choose View Hide Sidebar italic . ... holding the button then adding pressure; the more firmly you press the faster you move italic through the pages.