In Windows 10, the file type association for .pdf stops working after upgrading from Adobe Reader 2017 (Classic Track) to Reader 2020 (Classic Track). Issue occurs if file association was originally configured by DISM or user for previous Adobe Reader version. The same .pdf file association is expected to work with new Adobe Reader versions.

Double-clicking a PDF file displays Windows prompt "How do you want to open this file?". The HKCR registry key still contains an entry for the ProgID, AcroExch.Document.2017. Should the Reader 2020 installer remove the HKCR\AcroExch.Document.2017 registry key? Deleting the key appears to resolve the issue.

Steps to reproduce the issue:
1. Install Windows 10 Enterprise.
2. Install Adobe Reader 2017 (Classic Track) using bootstrapper installation (setup.exe).
3. Set default PDF program manually. This can also be applied using DISM during operating system deployment with XML containing the following entry; <Association Identifier=".pdf" ProgId="AcroExch.Document.2017" ApplicationName="Adobe Acrobat Reader 2017" />
4. Install Adobe Reader 2020 (Classic Track) using bootstrapper installation (setup.exe).

Bootstrapper Deployment
https://www.adobe.com/devnet-docs/acrobatetk/tools/DesktopDeployment/bootstrapper.html

Set Acrobat Reader or Acrobat your default PDF program on Windows 10
https://helpx.adobe.com/acrobat/kb/not-default-pdf-owner-windows10.html

Setting the Default PDF Viewer
https://www.adobe.com/devnet-docs/acrobatetk/tools/AdminGuide/pdfviewer.html#solution-1-dism

ProgID Key
https://docs.microsoft.com/en-us/windows/win32/com/-progid--key