How do you open the Microsoft Office Professional Plus file once downloaded to my computer? It gives options: "How do you want to open this file"  Internet Explorer, Notepad, Paint, Windows Media Player, Windows Photo Viewer, Word Pad, or look for another app on this computer.

if the downloaded file is in the ISO or IMG format, you can use a utility like MagicISO or WinCDemu, to "mount" the file as a virtual disc drive, then, run the setup.exe from the virtual drive.