Hi marthab48604416 ,
Please provide the exact dot version of the software & OS installed at your system .Also check whether is there any update available for the software after going through "help > check for updates "
Follow this thread to reset the preferences for the Acrobat software :- How to reset Preference settings in Acrobat.
Is this happening with all the files or with certain one.
Are those files are on network drive ? If they are, please save them on local drive & then check .