Using a WebBrowser control in a WinForms application, trying to view a PDF file in the control now causes the control to start Acrobat incorrectly as Acrobat says it cannot find the file. At that point the WebBrowser control is hung and in exiting the program a failure occurs trying to unload AcroPDFImpl64.dll, as indicated in the Event Viewer. Also, regardless of whether the default PDF app is Acrobat Reader or Acrobat Pro, it always tries to start Acrobat Pro.
Going into IE and disabling the Add-in fixes that failure. When the default app is Acrobat Pro, it will start it fine. When the default app is Acrobat Reader... if the Reader window is open it works OK, but if the Reader is not open then it will start the Reader but not show it. And then the Reader is no longer working and all instances must be killed via Task Manager.
The PDF Browser Control file AcroPDFImpl64.dll is the latest version 21.1.20138..29261 dated 2/14/2021.