This looks likes scab, which is a common fungal disease that effects both apple and pear trees.  You can control now by removing any damaged fruit that is still on the tree or on the ground around it.  If there are some undamaged fruit remaining, you may want to spray a fungicide such as Captan or Immunox to prevent them from developing this disease.  In future years, start your fungicide spray earlier in the year, around the time the trees are in blooms.  As with most diseases, the conditions of a given year (temperature, rainfall, etc.) will play a large role in determining how bad the disease is in any given year.  Please see the following publications for more details:

http://www.caf.wvu.edu/kearneysville/disease_descriptions/ompearsc.html

http://pubs.ext.vt.edu/456/456-018/Section_3_Home_Fruit-Disease_and_Insects-1.pdf