If you already have an ebook writing and PDF production workflow that you're happy with, you can upload a PDF directly using our Upload writing mode. This includes PDFs generated using LaTeX, or even those saved from Word.
With our Upload writing mode, you only need to upload at least one of PDF,
EPUB and MOBI. PDF-only is totally fine, especially if you're writing a computer programming book: PDF is still the dominant format for computer programming books. (If you were writing a novel, we'd strongly recommend uploading EPUB and MOBI as well: EPUB for phones, and MOBI for Kindles.)
If you already write in LaTeX and are happy with your workflow, the Upload writing mode is definitely the best option.
If you already write in Microsoft Word, you can either upload the Word document and see if our ebook generators can handle it, or you can upload a PDF directly using the Upload writing mode. The reason we support Word, and the supported formatting for Word documents, is explained further here: https://leanpub.com/blog/2016/03/writing-leanpub-books-in-word
Finally, note that we generate our own PDFs using LaTeX that we've produced from Markdown or Markua. Leanpub depends on LaTeX.