拓展 means both expand and develop in English,however,their usages are different.
Expand is to expand something physical,including the hardware.Therefore,we can use expand on a department,office,building or even the market.When we say to expand the market,we usually refer to the share of the market,not new market.
Develop is to develop something not physical and is deeper than expand.When we develop a market,we focus not only the market share but also those undeveloped parts of the market.We say to develop a software,but never expand a software.
When we say expand the office,we expand the physical space of the office.When we say develop the office,we refer to developing the capacity/ability of the soft components including human resources.