2019 version...I am able to open a two-side .pdf one page at a time. After fixing the file, I immediately save (not save as) the file to have acrobat open the two sided .pdf again. Since then, 2020 and 2021 versions, when I finish fixing the one side of the .pdf and save the file, I only see one side of the .pdf in acrobat. Is this something in the prefererences that need to be clicked on? in the later versions?