The fruit of pears always has stone cells scattered through it. Those cells give pears their slightly gritty texture. When pears still on the tree are stressed, they often develop clusters of stone cells, the hard spots you are noticing.
This disease is sometimes referred to as "dimpling" because of the symptoms observed on fruit. Symptoms begin as early as 3 weeks after petal fall, when dark-green areas form on the fruit. Cell growth surrounding these areas is restricted and, as a result, fruit become pitted, gnarled, and deformed. Pits are produced by others causes such as plant bug injury, mechanical damage, boron deficiency, or cork spot. However, pits caused by such factors are more superficial.
Heavily pitted fruit may become so gritty that it is difficult to cut the fruit with a knife. Some strains of the stony pit virus can cause a roughened bark or measles-like symptoms on the fruit. Dimpling and cracking of the bark, stunting of the trees and chlorotic vein banding or mottling have also been reported. Severely infected cultivars include Bosc, Comice, and Seckel. Obvious, but less severe, symptoms have been reported on Hardy, Conference, Forelle, Howell, Old Home, Packham's Triumph, Bartlett, Winter Nelis, and other cultivars.
Symptoms on fruit vary from season to season as well as severity. Trees that show symptoms one year may have no pitted fruit the following year.
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