Acrobat Reader error 0:521

Question

Hello,I'm experiencing a recurring Error 0:521 with specific and reproducible symptoms, hoping someone can provide insights or potential solutions. Error Specifics:Error Code: 0:521Affected Software: Adobe ReaderOperating System: Windows 10 or Windows 11Software Version: different versions, also with latests Detailed Error Behavior:Scenario Trigger: Opening a PDF from a web applicationInitial Action: Adobe Reader launches to view the documentClosure Sequence:After closing the documentAdobe Reader process remains active in Windows Task ManagerCannot open other PDF files due to persistent error 0:521 until the process is killed Would greatly appreciate any insights or potential workarounds. Thank you in advance for your help!

AnandSri · Answer

Hello,

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

Please ensure you have the latest version of Acrobat installed on the machine: 25.001.20428 Planned update, Mar 04, 2025. Check for any pending updates from the Menu > help > check for updates, install the updates, restart the app and the machine, and check. For more information, see this: https://adobe.ly/43y76TL.

For testing purposes, please disable Enhanced Security in the app's preferences by following these steps:

Go to Menu > Preferences > Security (Enhanced).
Uncheck Enhanced Security and Protected Mode at Startup.
Uncheck Run in App Container as well.
Click OK, then restart the app and your computer.
Try opening the PDFs.

After testing, please re-enable the security options. If the issue persists, please use the Acrobat Cleaner tool to remove the installed app, reboot the machine and install Acrobat Reader.

Let us know how it goes.

Thanks,

Anand Sri.

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