We are running the latest patched versions of the following
Windows 10 1809 OS Build 17763.914
Office 2016 Professional Plus 32 Bit 16.0.4266.1001
Adobe Acrobat Reader DC Version 2019.021.20058
The problem affects all documents that Windows decides have come from untrusted sources- eg files from Internet, email and even network drives. These files can be identified in file properties as below.
When a user tries to open an untrusted pdf, docx or xlsx files, Protected View should engage with standard office and acrobat security settings in place.
the user will experience a 5-10 minute delay in opening these documents, the application will freeze and will not open any document for this duration
We have managed to put a workaround in place disabling the Acrobat Secure app container using this reg key Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Adobe\Acrobat Reader\DC\FeatureLockDown\"bEnableProtectedModeAppContainer" = 0 (default is 1) and also by disabling the Protected View Features in Office as necessary to keep some users working but this is a significant compromise to our security profile and we need to revert those changes asap.