de.google.com/p/tesseract-ocr/">Tesseract</a>, and
      <a href="http://www.libreoffice.org/">LibreOffice</a> libraries.
      Poppler is used to extract text and metadata from PDF documents,
      PDFTK is used to split them apart into pages, and GraphicsMagick is used to generate
      the page images (internally, it's rendering them with
      <a href="http://pages.cs.wisc.edu/~ghost/doc/GPL/index.htm">GhostScript</a>).
      LibreOffice and GraphicsMagick convert documents and images to PDF.
      Tess