Modern versions of Office (Click-to-Run installations like Office 365) often install the VSTO runtime automatically in the background. You may not actually need to download this manually unless you are troubleshooting a specific error.
: The Visual Studio 2010 Tools for Office Runtime is the standard installer for VSTO 4.0. vsto 4.0 download
: If you are a developer looking for the redistributable package to bundle with your software, use the official redist link. use the official redist link.