When was the last time you had to (God forbid!) dig around for a manual to a dishwasher, washing machine; dryer, or any number of home entertainment devices? It's a very organized person who can lay hands on exactly what they need in a timely manner in just about any house. If you are one of those, my hat is certainly off to you!
The last few manuals I needed (and couldn't find around the house) ended up falling in my lap (literally) via the Internet. It is amazing what a simple Google Search using your model number and the words user guide or owners manual in the search terms can turn up. In less than a minute I had exactly what I needed, and a minute later it was on my Kindle Fire safely tucked in the documents folder. That is where you put files your Kindle Fire can open but you didn't get them from Amazon. When you turn on your Kindle Fire, touch docs instead of books and if your Kindle Fire can read it, it will be listed.
I have to say... the Kindle Fire does great pdf files! And the Internet? Well I found an owner's manual for a 40+ year old Singer sewing machine.
So... look around, for pdfs with your Kindle Fire in mind... you will be surprised what you can find!