I figured out that putting pears in the fridge is the best option for keeping them preserved. The first 3 days there was no changes, but on the forth day the pear of the porch got its first new brown spot. Only on the beginning of the second week the pear in the fridge started to have some visible changes. I also realized on the second week the pear outside was starting to get soft but the one in the fridge stayed pretty hard.