A running instance of Acrobat has caused an error

Hello Sabrina!

I hope you are doing well, and we apologize for the delayed response and the trouble.

Have you tried the solutions in this help article? Failed to connect to DDE Server. If not, please follow the suggested steps and let us know the results.

Ensure that your operating system has all mandatory and optional updates installed. After updating, restart your machine and try opening the PDFs again.

Could you confirm if you're using Windows or Mac? Also, does this issue occur with a specific PDF or all PDFs? If the problem persists, try using the Acrobat Cleaner Tool to remove all installation files, restart your machine, and reinstall Acrobat or Acrobat Reader.

For troubleshooting, you can create a new test user profile with full admin rights, install Acrobat/Reader, and check if the issue continues. Additionally, try disabling security settings:

1. Windows: Go to Menu > Preferences > Security Enhanced.
2. Mac: Go to Acrobat > Preferences > Security Enhanced.
3. Uncheck Enable Enhanced Security and Protected Mode at Startup.
4. Click OK, restart Acrobat, and reboot your machine.

Let us know how it goes.

Thanks,

Anand Sri.