The good news is that it doesn't look like pear rust or fireblight or alternaria or powdery mildew or scab or canker, which are the well known horror fungus problems. So I'm suspecting animal. It might be pear leaf blister mite. Try to see if you can see some mites under a magnifying glass. This suggests it isn't too terrible a thing to have, you could just remove affected leaves by hand. Garden pests - how to deal with pear leaf blister mite on pear trees | Problem solving | How to | BBC Gardeners' World

You probably won't be getting fruit off it this year, so you could use a systemic insecticide if it seems to be badly affected.