Hi and welcome to the forum!
Better avoid the OOXML format, have a look at: MS Office 2007 OOXML file format (docx, xslx, pptx, ppsx)
Standards like ODF (native format for OOo) have been designed for interoperability.
NB: LibreOffice has decided to support OOXML. Not the best decision IMHO. OOo could save in OOXML but it was the team's decision not to allow that.
AOO 4.1.2 on Xubuntu 15.10 (Wily Werewolf) and PortableApps port 4.1.2 on Windows 7