So earlier today I was trying out Microsoft’s online office suite and noticed something interesting. Whenever you create a new Word, Excel, or PowerPoint file from the OneDrive interface, it automatically creates it using the OpenDocument file format (odt, ods, odp) as opposed to the Microsoft Office format (docx, xlsx, ppt). Interestingly if you create it from Office.com it uses the Microsoft format instead.
Kyle Piira 
4 replies on “Microsoft Office Online switches to OpenDocument as default format”
You can change the default file formats for Office documents from your OneDrive Settings. There is an option called Office file formats.
Oh yeah look at that! Somehow it must’ve been switched over to OpenDocument (I’m not complaining).
Interesting… I can’t help but automatically assume this is a glitch of sorts, or possibly a default setting was changed.
Looks it is a setting in OneDrive that I must’ve changed at some point.