Does the tree it’s self look healthy? Some pear fruit just look abnormal, like the fruit of this variety right here Duchesse D' Angouleme Bronzee / Duchess D’Angoulme pear
This different variety with a very similar name also not the average pear shape, also with a similar brown and green color as the pears on your tree Largest / Best tasting pear - #25 by clarkinks
This is a variety found in the UK, yet the brown in this variety is usually coming from the area near the stem, yet it’s the closest thing appearance wise that I have seen so far to what you have Pitmaston Duchess Pear Trees - Chris Bowers & Sons.