Preview PDF files

A few days ago, I lost the ability to preview PDF files in my directory. I have Windows 10. I can still preview every other kind of file. I have confirmed that my "preview pane" is selected in my directory. I have Adobe Acrobat Reader DC version - where I've already selected preferences: "Enable PDF thumbnail previews", and I've run "repair installation" and "check for Updates" under the Help section. Any other suggestions?