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Outdated Acrobat version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.
