I have difficulty deleting an Adobe Acrobat .pdf file after upgrading to Windows 10

If Windows Explorer is open turn off  the Preview mode.

You need to make sure the PDF file is fully closed and not still attached to a certain application. I found that unless I close Acrobat program, only then would the file be able to be deleted in Windows File Explorer. There does seem to be a time delay though from the time a PDF is closed and the time you select delete, depending upon where the file is being stored, say maybe on a flash drive, or in One Drive. That might have to do with the normal sync times that happen with Windows 10. Not 100% sure, but just trying making sure the file is closed and no other application has some sore of attachment to the file.