Update: This is NOT for fixing corrupt icons - this is for changing icons, corrupt or not.
This is NOT for the library icon nor for the Metro icons. This is for Windows 8 Explorer icons.
I'm able to change the default program from control panel or right click file in Explorer => properties. But I can't see a way to change the icon itself. I'm putting a screenshot of what I'm presented - the same holds true for PDF files or any other files.
Edit: Even when I try to change the icons of shortcuts, I'm unable to do so. Weird!