Hi, While Acrobat Standard or Professional permits an "initial open" configuration that displays the Bookmark pane and the PDF page, Adobe Reader does not.
With a PDF open use Ctrl+D or command+D to open the PDF files's Document Properties dialog. Alternatively, click through: File > PropertiesIn the Document Properties dialog you will observe several tabs across the top. Select the tab "Initial View". There are three panes here. The top pane (Layout and Magnification) has drop-down menus associated with three of the four configuration options present. For the 'Navigation tab' entry one menu choice is "Bookmark Panel and Page".
While Acrobat Standard or Professional permits an "initial open" configuration that displays the Bookmark pane and the PDF page, Adobe Reader does not.
Be well...
Be well...