If you are having difficulty opening PDFs on Windows 10 you are not alone, as Microsoft has released an urgent fix to address the issue.
Microsoft has released an out-of-band Cumulative Update KB5004760 for all supported versions of Windows 10 to address the following problem:
Updates an issue that might prevent you from opening PDFs using Internet Explorer 11 or apps that use the 64-bit version of the WebBrowser control. Additionally, a PDF might render as just a gray background when using the Adobe Acrobat plug-in.
The update will also remove Flash from your machine.
If you are experiencing issues you can find the update under Optional Updates when you check for updates in Settings or download it from the Microsoft Catalogue here.