There are two Kindle Fire HD's. The newest one lacks a front webcam. If yours has a camera, it is the older one. Comparison table here:
http://en.wikipedia.org/wiki/Kindle_Fire_HD
I would check xda-developers.com to find out about jailbreak/rooting, though if you want to install custom fonts for the Kindle reading app, I'm not sure that's something anyone has bothered to do. There are several Android reading apps that let you use custom fonts without any rooting, and if you are building your own ebooks, another option is to embed fonts.
Hacks for Kindle 2/3/4 have absolutely no application to Fire HD.