Quit Acrobat.
Last updated on
Sep 23, 2025
Learn how to troubleshoot a running instance error in Adobe Acrobat on Windows.
You may encounter the following error when you try to open a PDF or use a tool while another instance of Acrobat on Windows is already running:
A running instance of Acrobat has caused an error
Unresponsive background processes
Press Ctrl + Shift + Esc to open Task Manager.
In the Processes tab, locate Adobe Acrobat under Apps and Background Processes.
Right-click each Adobe Acrobat process and select End task.
Close Task Manager and relaunch Acrobat.
Incorrect registry entry
Quit Acrobat.
Press Windows + R to open Run.
Type regedit and press Enter.
Navigate to HKEY_CLASSES_ROOT\acrobat\shell\open\ddeexec\application
Right-click the application folder and select Export. Save the backup file.
Double-click Default in the right pane. In the Value data field, change the value from:
AcroViewA20 to AcroViewR20
Select OK and close the Registry Editor.
Relaunch Acrobat.
Outdated Acrobat version
Open Acrobat.
Select Menu > Help > Check for updates.
Install available updates and restart Acrobat.
Corrupt installation file
Open Acrobat.
Select Menu > Help > Repair installation.
Follow the on-screen instructions to repair the files.
Restart your system after the repair is complete.
Work smarter with Acrobat on your desktop
Create, edit, and organize PDFs with powerful tools that help you stay productive anywhere.
