Non-DRM Mobi books, like free e-books found online in Mobi format, or files you convert to Mobi files, are already supported on Kindle.
Kindles can read a variety of non-proprietary, non-DRM'ed formats. They read TXT, HTML, JPEG, and non-DRM Mobi files directly.
Use Mobipocket software to convert PDFs to that format so you can read them on Kindle.
The Kindle supports Mobipocket files directly. You don't need to write a script to do that.
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