TO calculate the value of a Bond Forward Contract, we take the PV of Ft-Fo, however wouldnt you just subtract Ft - PV of Fo since Ft is already in present value form??
Ft(T) is the new price you’d be contractually allowed to buy/sell at at t = T if you entered into that contract today (t) to offset your initial position at t = 0. Because the prices you locked in at Fo(T) and Ft(T) (to offset the original) only actually take place at t = T, the difference between the two has to be discounted to today (at t = t) to find the value to the long or short party. Hope that helps!