When I’m prepping a book for distribution, I treat converting PDFs to mobi like a two-part job: rescue the text and then dress it up for devices. PDFs are great for print but awful for e-readers because they lock layout. So my first move is always to get a source file that’s reflowable — Word, HTML, or EPUB — rather than trying to force the PDF into a mobi and hoping for the best.
Practically, I usually start by opening the PDF in Adobe Acrobat (or a free OCR tool if it’s a scanned file) and exporting to Word or clean HTML. That gives me a text file I can tidy: fix headings, make a real table of contents, remove headers/footers, and ensure images are placed and sized correctly (downsample big images to 300 dpi). If the PDF was a simple typeset manuscript, rebuilding in Word or a clean HTML/CSS file is faster than fighting conversion quirks.
Once the source is clean, I convert to EPUB using Sigil or Calibre, or export directly from Word to EPUB. Then I use Kindle Previewer or Calibre to convert that EPUB to mobi (older devices) or to check how it will look on various Kindle screens. For comics or heavily designed books, try Kindle Comic Creator or create a fixed-layout EPUB so panels don’t break. Always test on an actual Kindle or the Kindle Previewer app and proof the TOC, links, and widows/orphans. Metadata, cover image, and proper filename conventions matter too. If I’m uploading to Amazon KDP, I usually upload EPUB or DOCX since KDP prefers those now, but I keep a mobi for direct sales and compatibility with some older readers. In the end, patience with clean source files saves hours, and a quick proofread on device will catch the weird stray line breaks that sneak in during conversion.