Is an office obligated to have a Mezuzah?
An office shares the same status as a store and is hence to have a Mezuzah placed without a blessing.
Is the entrance of an office building obligated to have a Mezuzah?
An office building which contains Jewish offices is to have a Mezuzah placed, without a blessing, on all the doors leading to the office. If however there is fear that doing so will cause enmity with the gentiles, or will lead to the stealing of the Mezuzah’s, then it is completely exempt.
 Pischeiy Shearim 286/106