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.
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