LibreOffice doesn't, as far as I'm aware, have any issues reading DOCX files. The only issue I've ran into is PowerPoint presentations created with MS Office. That being said, here are two options I recommend.
1) CutePDF - It creates a fake printer, that when you send a print job to it, just converts the print job to a PDF document. It is free software.
2) LibreOffice - The continuation of OpenOffice by The Document Foundation, it has native PDF export capabilities, and works perfectly fine with most MS Office documents (except MS Office created PowerPoints as I said above). LibreOffice is free and open source software.