Adobe Reader is not set as the Default PDF Handler – If your default PDF viewer is not configured to be the default PDF handler and the PDF thumbnail preview feature is not enabled, expect to see this error in when attempting to preview PDF files in Outlook.

In this case, you can fix the issue by forcing Adobe Reader to run in Compatibility mode with Windows 8. Adobe Reader runs on Windows Server – This error is very common in instances where the user tries to use the preview capabilities of Adobe Reader on a Windows Server version (most commonly Windows Server 2016).So if this scenario is applicable, you can fix the issue by opening Adobe Reader and accepting Accepting the EULA. As it turns out, Adobe EULA’s needs to be accepted before the application is able to preview files externally. Adobe Reader’s EULA wasn’t accepted – Another scenario in which this error will occur is a new Adobe Reader installation that was never opened before.Some users facing this issue have managed to get it fixed by accessing the LAN Settings and disabling the Automatically detect settings option.

Internet Auto Detect is Enabled – As it turns out, one potential cause with the potential of causing the PDF Preview Handler error is a setting called Internet Auto Detect.

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