As you have mentioned the error message above, it seems that you get this error when you try to open the Adobe Acrobat Reader DC.
Try the troubleshooting steps provided here Fatal error - Acrobat failed to connect to a DDE server for this issue.
Check if that helps.
If you still experience the issue, please share the details asked below:
-Adobe Acrobat Reader DC's dot version (Take help from the steps mentioned here Identify the product and its version for Acrobat and Reader DC )
- OS installed on your machine.
-Did you make any changes to the application after which you have started to receive the error message?
Let us know if you need any help.
We will be waiting for your response.