Step 1: Open Task Manager
Press Ctrl + Shift + Esc on your keyboard at the same time.
This will automatically launch ‘Task Manager’.
Step 2: View Running Processes
Make sure you are viewing the ‘Processes’ Tab
Step 3: Locate Adobe Processes and End Task
You may see it in ‘Apps’ and you may see it in ‘Background Processes’
Right Click it and Click ‘End Task’
Afterwards please try to open Adobe or a PDF again.
Alternatively, you can restart your computer which will also end the Adobe processes giving the error.