If you are having problems with Office 365 document features not working like :
-Edit Mode
-Collaboration Mode(multiple folks editing doc)
-Open in Browser
This can be caused when using older Office document formats. Office documents saved for older versions of Office may need to be reopened and then use 'save as' to save them as the newest format:
Word -> .docx
Excel-> .xlsx
Powerpoint-> .pptx
Documents saved with the older .doc, .xls and .ppt formats are unable to work with many of the newer Office 365 features until resaved as the newer format.