The Output Pane allows you to view any errors related to JavaScript or document processes.
This pane is a context-aware element, and its tab is in the side-bar if there are JavaScript or other errors when opening or using the PDF file.
It opens automatically to alert you of any important output messages.
Click on the Output tab in the side-bar.
Click on the Output tab on the side-bar to open the Output pane
Click the Clear to reset the Output Pane