Current Microsoft Windows operation systems are mostly 64-bit editions. For Microsoft Office the 32-bit edition is still the default architecture.
Office versions (e.g. 2016 professionell plus) can be downloaded as ISO from MSDN. Often the ISO contains 32-bit and 64-bit setups on one single ISO image, not like the operation system where you can download a ISO for the x86 and an ISO for x64.
The setup of office will “decide” by itself which office version will be installed on …