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.
Please check whether you are getting the same behavior with other files as well.
Also after signing in to 'cloud.acrobat.com', check with the option for 'send for signature' & is same error appears then check with other Internet Browsers as well.
After trying these steps if issue still persist, please go to 'adobe.com/getsupport' after signing in select the option for 'still need help contact us' then initiate a chat session. The chat expert will help you using the Tools in this case .