You receive an error that you are not able to delete a PDF because it is open, when it is not open.

When explorer preview is on, and Acrobat is installed, the preview pane will open the file behind the scenes, not allowing you to delete PDFs.

To work around that, temporarily turn off the preview pane

1. Open a File Explorer, or any folder
2. Go to View then disable preview pane by clicking Preview pane