Opening View of Documents - Frustrating Panes!!!

When I open a document, either from an email or from my own computer, a large percentage of time I see a pane on the left side of the screen for Page Thumbnails, Bookmarks, etc.  This pane takes up over half the screen and it's a very, very annoying thing to have to clear it every time I want to view the document.  Some files don't open like this.  I would say about 80% of the files now opens with this pane.  I've tried all the setting adjustments I've seen on YouTube and other chat sites.  None of them are working on a consistent basis.  The same thing keeps happening on about 80% of the documents I open.  Is there something I can do to correct this so those panes don't ever show unless I want them to?