Need to replace Arial, Times Roman with Calibri in the entire book (FM 10). Please let me know the script for this. I am very new to this.

Hi, I'm sorry no one has replied yet. Have you found an answer to your problem? 

I don't work with books, but my first thought was – couldn't you change the fonts in the paragraph styles in the template, then just reapply the template to the book? You wouldn't need a script to do that. (But maybe books don't work like that.)