Fahrenheit 451 reading

As I began reading chapter 2 of the book I found it quite interesting. Montag's attitude toward books changes completely. After having watched the woman set herself on fire rather than be taken away, really affected him. He took a book for himself and hid it. However, he had collected books before, which were hidden in the ventilator shaft. I don't understand why he had books previously to the time when Millie discovered the book behind his pillow.

Once he lit the flame of his determination to make books a popular pastime, he doesn't seem to let fear or obstacles block him from his goal.