When Windows needs to draw an icon, it uses the copy from the cache instead of retrieving the icon image from the original application file.
After you install Acrobat or Reader on Windows 7 or Vista, icons of all applications and file types change to Acrobat/Reader icon. File sharing is turned off, so I don't know what is causing it. I never set up sharing for anything because, well, there's only me and this 1 computer. I can remove it from individual files through windows explorer share button, but not all of the files at once. Unlike in Windows 8.1, One Drive in Windows 10 doesn’t use placeholder files to indicate files that are online only.Instead, you see only the files you choose to sync to your computer.