Thumbnail preview of PDFs not displayed in Windows Explorer - Fix
After the Feb 9, 2021 release of Acrobat & Reader DC version 2021.001.20135, Thumbnail preview of PDFs were not displaying/generating in the Windows Explorer.
The thumbnail preview of PDFs was not displaying/generating correctly in the Windows Explorer even though the Enable PDF thumbnail previews in Windows Explorer option was selected in Edit > Preferences > General.
Note: This is a temporary workaround, Adobe is working to fix this issue asap.
Quit Acrobat Reader DC if it's already running.
Open the Registry Editor: Go to Run (Windows menu + R), type regedit.exe in the Open field, and then click OK.