I'm using LibreOffice4.0 UNO to convert files. I managed converting between doc and docx, from xlsx to xls and from docx to doc, but I'm having trouble finding the FilterName value for XLSX and PPTX.
propertyValues[0] = new PropertyValue();
propertyValues[0].Name = "FilterName";
propertyValues[0].Value = "...";
for doc I used: "swriter: MS Word 97";
for docx I used: "Office Open XML Text";
for xls I used: "swriter: MS Excel 97";
for ppt I used: "swriter: MS PowerPoint 97";
Thanks.
For XLSX you can use either Calc MS Excel 2007 XML
or MS Excel 2007 XML
.
I also found this for OpenOffice but I'm not sure if it works for your case:
DOCX - MS Word 2007 XML
XLSX - Calc MS Excel 2007 XML
PPTX - Impress MS PowerPoint 2007 XML
There is a BIG list here