This issue is a programming bug confirmed with Adobe's Rick Borstein which causes it to not correctly autosize the file thumbnail images pane to reveal the vertical scroll bar. We hope Adobe will fix this issue soon. Until then, you will have to adjust this pane by performing the following steps.
Find the vertical pane size adjuster tool. Click on it, drag it to the right until the vertical scroll bar is shown. Or, if your mouse has a scroll wheel, move your cursor over the thumbnail images and scroll up/down to access the desired document.
End of instructions.