Do you have an e-book or a collection of e-books that you want to transfer (side load) to your new Kindle Fire? If you've already tried transferring them, you may have noticed that some or all of your e-books show up under the "Docs" heading, instead of "Books."
The benefit of having your e-books listed under "Books" is that you can sort them by author. Under "Docs," you can only sort by recent or title. If your collection is a modest one, this might not bother you a whole lot. If, however, your collection is rather sizable, you might want the extra sorting option. Here's how to get side loaded e-books to show up under "Books" on the Kindle Fire:
Step 2: Add your e-book(s) to Calibre.
Step 3: Highlight the e-book or e-books that you want to transfer to your Kindle Fire and click the "Convert books" button.
Step 4: When the convert window appears, make sure that the output format is set to "MOBI."
Step 5: Click on "MOBI Output" from the left column and delete the [PDOC] tag in the "Personal Doc tag" section.
Step 6: Click the OK button to start converting your e-books.
Step 7: Once Calibre has finished converting your e-books, copy your e-book files to the "Books" folder on your Kindle Fire. Remember, you'll need a micro-USB data cable (not included with the Kindle Fire) to transfer files to your Kindle Fire.
Step 8: Check the "Books" section to make sure your e-books are there.
That's it. To delete the PDOC tag permanently in Calibre, go to Preferences > Output Options > MOBI Output and remove the tag there.
A side benefit to converting your e-books in Calibre, is that it shrinks the size of the Mobipocket file (.mobi). Since the Kindle Fire doesn't have any memory expansion slots, converting your e-books may end up saving you a lot of storage space on your Fire.