unoconv
Universal Office Converter - Convert between any document format supported by LibreOffice/OpenOffice. http://dag.wiee.rs/home-made/unoconv/
Support was added to Tiki19, and improved in Tiki20. This permits pretty much all file formats to be converted to PDF, and then viewed via PDF.js viewer.
How to activate
In tiki-admin.php, activate the preference View or export office documents as PDF (fgal_convert_documents_pdf)
It requires dependencies to be installed. The admin panel will indicate if you are missing anything.
See also: Media Alchemyst
Initial commit: http://sourceforge.net/p/tikiwiki/code/68422