Calibre

E-book library management application built around organizing, converting, and reading large personal e-book collections; its bundled `ebook-convert` CLI happens to double as a capable PDF-to-plain-text (and PDF-to-other-e-book-format) converter, alongside dozens of other supported formats. Not a PDF-specific tool — PDF is just one of many formats its conversion pipeline handles — but a genuinely useful one when PDF-to-text conversion is needed as part of a broader e-book workflow.