Calibre is a free and open source e-book library management application developed by users of e-books for users of e-books. It has a cornucopia of features divided into the following main categories: Downloading news from the web and converting it into e-book form; Library Management;E-book conversion;Syncing to e-book reader devices; Comprehensive e-book viewer; Content server for online access to your book collection. It supports:
Input Formats: CBZ, CBR, CBC, CHM, EPUB, FB2, HTML, LIT, LRF, MOBI, ODT, PDB, PDF, PML, PRC^, RB, RTF, TCR, TXT
Output Formats: EPUB, FB2, LIT, LRF, MOBI, OEB, PDB, PDF, PML, RB, RTF, TCR, TXT.

Tutorial: How to Convert Kindle Files to PDF Step by Step?
Step 1: Download and install Calibre. It supports Windows, Mac and Linux.
Step 2: Launch Calibre. Then click the top left button "Add books" to add Kindle books.
Click the "Formats" item, Calibre will tell you if this Kindle file is protected by DRM or not. If it's protected by DRM, you need to use kindle drm remover to remove AZW DRM. If not, you can convert the convert kindle books to pdf easily with Calibre, just go to the next step.
Step 3: Click the "Convert e-books" button. At the top right of the pop-up window, click the drop-down arrow for "Output format". Select your needed output format, here you need choose PDF as the output format.
Step 4: Lastly, click "OK" button to Kindle books to PDF.

Related: freeware drm removal , free drm converter