Turn a MOBI ebook into a PDF with real text and images - here in this tab, with nothing uploaded.
Old Kindle-format books are often the only copy of something you own. This lays the book out in your browser and saves it from the print dialog, without sending it anywhere.
Your browser lays the book out as pages, and its print dialog is where you choose 'Save as PDF'. That gives a PDF with real, selectable text and sharp images, not pictures of pages.
Only if they have no DRM. Copy-protected books are encrypted, and removing that is not something this site does. Books from Project Gutenberg, Standard Ebooks, Humble Bundle and most indie stores are DRM-free.
Use AZW3 to PDF - it is the same tool, set for the newer Kindle format.