The bitness of the VSTO Runtime must match the bitness of the Microsoft Office installation, not necessarily the Windows operating system.
: Typically, if you install a 64-bit version of Office on a 64-bit Windows OS, this runtime is installed automatically alongside it. Official Resources For documentation and downloads, you can refer to: microsoft visual studio 2010 tools for office runtime -x64-
# CheckVSTO.ps1 # Verifies VSTO 2010 Runtime is installed and registers a sample add-in The bitness of the VSTO Runtime must match