How to reduce margin of pdf for printing two pages per page with big letters?

Hello, I am using Acrobat Pro X on a Mac. I have been trying to print the pdf version of a book. When I printed two-page/page on a letter size paper, the letters became very small. I scaled up and parts of the pages got cropped off. I noticed that there are still a lot of empty area in the margins. I have been trying to reduce the margins so that I can fit two pages on a page with comfortable letter size. I have spent hours trying various parameters without success. Could you please help?