Adobe won't open from taskbar

Download a pdf file.  Adobe shows document is open when cursor hovers over adobe icon in taskbar.  But adobe will not open when I click on the icon.  Even without a document, adobe will not open from anywhere on computer.  Go to "All Apps" double click on adobe and it seems that it opened, but it doesn't.  Again, it shows open in taskbar but can't get it to open in a windows tab.  The only way to open adobe is to click on the icon, then go to another window, shrink it to half screen, then windows shows all the other open tasks and adobe can be selected.  Then it will fill second half of screen and can be maximized to full screen.  Once done, other documents can be opened.  Right now, hovering over the icon shows that two documents are open but I can't get either to go full screen unless I do the half screen thing above.