>We are planning to extend wifi to remote area, This remote area is of 600 feet and 300 feet away from office building.
Until I read @Uberseehandel comment I did not click you were trying to support client access devices over this range. My gut reaction is to tell you not to attempt this. @Uberseehandel is right - the client devices are not going to have antennas that are going to be able to send a nice signal back.
If you want to persue this lets aim for a low data rates, like 2Mb/s. It is only going to be able to handle very low bandwidth demands. I would also only think about using 2.4Ghz.
Are you able to put some APs closer to the users in MESH mode? You could use directional 5Ghz client for the backhaul and the 2.4Ghz to serve the clients.
Next option is to use multiple APs with narrow focused sector antennas to reduce the area they can see. I would consider something like this 11dBi 2.4Ghz sector antenna. Perhaps a pair of MR74's with these antennas offset by maybe 20 or 30 degrees. I think these maybe indoor antennas, so you may need to put them into a waterproof enclosure if they are going outside.