Looks like a fungal infection. Pick off the affected leaves if you can and throw them away with your household rubbish.

DO NOT compost them.

Try using a fungal spray on the tree (if the tree is not too big.)

Did the leaf damage first start off with little pink or reddish bumps before turning into larger dark patches? If so, then this could be pear leaf blister mite. If it is then it's an insecticide that's needed, a fungicide would be of no use.

Pear leaf blister mite is considered more of a cosmetic problem rather than something that will permanently damage your tree. Using an insecticide for leaf blister mite is applied more as a preventative measure than a cure. You need to apply it at bud break for it to work.