+1  A: 

The web page XSLT Transformation should contain the information you are looking for (as well as a basic example). The general answer is that you have to unzip the file first, but the unzipped content should be amenable (although content and presentation are stored in different files). Since you are mentioning content.xml I gathered you already know this; and the link is to a page that transforms the content.xml portion of an .odt file.

Kathy Van Stone
+1  A: 

XSLT is designed to perform transformations of XML documents, one of the possible transformation results is HTML, content.xml is... well, an XML document. Therefore you can transform it.

Ihor Kaharlichenko