Unable to open PDF. Something went wrong. A running instance of Acrobat has caused an error.

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Bug summary: There is an ongoing issue with the most recent update for Acrobat (version 24.005.20421) that may prevent you from opening PDFs after they have been saved to a network location. The error message: "A running instance of Acrobat has caused an error" comes up when trying to open a file from the network and if you check task manager there will be several (depending on how many times you tried to open the PDF) Acrobat tasks running in the background. 

Fix/Workaround: (Windows only) End any "Acrobat" tasks in task manager and then add (or update) the DWORD "bWinHttpNativeInProtectedMode" value to 1 at registry key path: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Adobe\Adobe Acrobat\DC\FeatureLockDown, then restart the computer.

Per Adobe support: "This DWORD is used because there’s a difference in how Acrobat makes network calls. The Windows SDK provides two methods for this—WinINet and WinHTTP—and this adjustment ensures compatibility".

Adobe says this "fix" will be included in the March update, which could be anywhere from March 1st to 31st with their update schedule.

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Update from Adobe support:

If the fix/workaround above does not work, try implementing these additional reg keys and then log out and log back in or restart the computer to refresh the registry:

HKEY_CURRENT_USER\SOFTWARE\Adobe\Adobe Acrobat\DC\Originals
Type: DWORD_32 "iMaxCosDocCache" Value: 8388608

HKEY_CURRENT_USER\SOFTWARE\Adobe\Adobe Acrobat\DC\Private
Type: DWORD_32 "bUseCaching" Value: 1

HKEY_CURRENT_USER\SOFTWARE\Adobe\Adobe Acrobat\DC\FormsPrefs
Type: DWORD_32 "bAutoCorrectTabOrder" Value: 0

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Adobe\Adobe Acrobat\DC\FeatureLockDown
Type: DWORD_32
"bWinHttpNativeInProtectedMode" Value: 1
"bEnableAutoSpellCheck" Value:0

[interesting_fireball4225]

Acrobat update 25.001.20428 did not fix this issue and neither did the registry edits.

Update 2 from Adobe support:

Adobe recommended trying 2 additional registry edits.

HKEY_CURRENT_USER\SOFTWARE\Adobe\Adobe Acrobat\DC\Private

Type: Dword_32 "IsRenderingPerfImprovementsEnabled" Value: 1
Type: Dword_32 "RFLFixForRenderingPerfImprovements" Value: 1

[ADCP_COMPROF]

Thank you. Yes the DWORD fix solved the problem. The actual Adobe fix instructions should include these suggestions because the various options did not work. Cheers ADCP

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After further troubleshooting with Adobe they provided an additional registry key DWORD "bFilePathPreprocessingUseFileHandleEnabled" which they say should fix this issue until it is definitively resolved in a future update.

Adobe also said two of the previous registry keys they recommended were not needed in this workaround.  The only registry keys that should be needed, with the most recent Acrobat version installed, are listed below:

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Adobe\Adobe Acrobat\DC\FeatureLockDown 
Type: DWORD_32 "bFilePathPreprocessingUseFileHandleEnabled" Value: 1
Type: DWORD_32 "bWinHttpNativeInProtectedMode" Value: 1
Type: DWORD_32 "bEnableAutoSpellCheck" Value: 0

HKEY_CURRENT_USER\SOFTWARE\Adobe\Adobe Acrobat\DC\Private
Type: DWORD_32 "bUseCaching" Value: 1
Type: DWORD_32 "IsRenderingPerfImprovementsEnabled" Value: 1
Type: DWORD_32 "RFLFixForRenderingPerfImprovements" Value: 1

[AnandSri]

Hello!

I hope you are doing well. Thank you for sharing the detailed steps that worked for you. We also have an article that contains the solution to the issue; for future reference, you may refer to this article.: https://adobe.ly/4491Bex

Regards,

Anand Sri.