Please let me know the following details:
1. Are you using Adobe Acrobat or Adobe Reader.
2. Which version of the application is installed on your system? You can check the same by going to Help > About Adobe...
3. Which OS are you working on?
4. Does the message pop up while opening any PDF or a specific one.
5. Does launching the standalone Adobe Reader application without opening any PDF also result in the same behavior.
6. Which Antivirus software are you using. Does disabling the same help?
Also, please try repairing the application from within the Control Panel after deleting all the files and folders from the installation directory.