If you don’t have your Windows 7 disc handy—but want to create a custom installation, run Windows from a USB drive, or just do a fresh install—you’ll need an ISO file of the disc. You used to be able to download them from Digital River’s servers,
but those links no longer work. Now, Microsoft has a Software Recovery Center where you can download those ISOs for free.
If your computer came with Windows, however, it’s probably an OEM version, which will not work on Microsoft’s new site. Instead, if you want to reinstall Windows without the bloatware, you’ll probably need to borrow a disc from someone and use your product key when you resinstall.