Pears turning brown from bottom
The closeup of a single pear looks like russeting. Russeting is an abiotic disorder which has a cluster of causes, including weather, variety and fungicide use. The fruit should still be edible. Here is a reference:
However, the picture of the whole tree gives me pause and makes me think this might be blossom end rot:
Unfortunately, BER will damage the fruit (and has equally mysterious causes).
You should be able to tell the difference between these two disorders. Russeting will not affect the fruit, but BER will.