Not sure what you mean by office network. Is this a network that someone else has set up and administers?
If yes, you would need to check with the network administrator to see whether or not a router like the AirPort Extreme would be allowed to connect to the network.
If yes, the AirPort Extreme would need to connect using an Ethernet cable from the WAN "O" port on the AirPort Extreme to an available Ethernet port on the network.
You don't mention what service you want the AirPort Extreme to provide. What might that be?