How can I print forces from external flow like, pressure forces, viscous forces etc, thanks

From a converged solution you can print pressure forces and viscous forces (as well as total force and the same three in coefficient form) by going to Report->Forces.

While the solution is iterating you have the option built into fluent to print the total force coefficient (Viscous + Pressure force) in two directions as well as a single moment about one of the primary axis (x, y, or z). You can turn this on by going to Solve->Monitors->Forces. This is good for monitoring your model convergence, and I highly recommend doing it if you aren't already. It's not as detailed as going to Report->Forces, but it's still very useful. If you want more than that though you'll have to use a UDF, but I'm unfamiliar with how to actually go about doing this. I've personally contacted Fluent about increasing the options for force monitoring, but they just shrug it off and tell me to write a UDF.

Also, make sure your reference values are set up properly (Report->Reference Values).

Hope this helps, and good luck, Jason