Ok I have a server which has plenty of contents stored inside and I need iPad to send a command to arduino which has been programmed to take out specific data that I'm asking from my iPad.
Your Arduino can't read or write to your PC directly so you'll need to be running some software on the PC that will respond to the request that's sent from the Arduino. This software on the PC will presumably also present a catalog of what's available via the Arduino back to the iPad so it can be selected in that app.
I don't know how will arduino be connected to PC as the wifi will be use to send data to iPad. Can the wifi work both ways?
Sure. WiFi doesn't need to be peer-to-peer.
Can the project be done?
You'll need to code something at the PC end, in the middle on the Arduino and on the iPad end. It sounds like a load of work for something that, so far, I still can't see why the Arduino is involved. There are inexpensive iOS apps that can let your iPad see SAMBA/Windows shares, and of course Dropbox is free if you just want to get to some files on your PC via your iPad and vice versa.
But, if it's just to prove that you can, I get that too...