Don’t you hate loading Open/LibreOffice.org? I do, so anything that helps to avoid the wait for the mammoth to load is good. Carlo Daffara shared a useful tip on Google+.
to convert files to PDF using libreoffice from the command line, I use this:
$ libreoffice –headless -convert-to pdf:writer_pdf_Export <filename>
works quite well, and in latest libreoffice releases quality of converted presentations from OOXML is substantially improved.