After some research, John discovered that an ISO file is essentially an image of a CD or DVD, which can be used to install software. The index of MS Office 2007 ISO refers to a list of files contained within the ISO image. This index is crucial in verifying the authenticity and integrity of the downloaded file.
The Internet Archive ( archive.org ) hosts many "abandonware" ISOs. Because Microsoft has not aggressively pursued these for Office 2007, you can find clean ISOs here. index of ms office 2007 iso better