Opening a document in Office 365 is accomplished in a variety of ways. One way is by selecting the program the document was created in, such as Word and seeing if it is listed in the Recent documents listing.
Once the document is opened, it is not automatically available for editing. The Edit Document button will need to be selected and then select the editing option desired.
The document can be edited in the desktop version of the software, if installed on the computer, or it can be edited in the online version of the software. When editing the document, it will automatically save changes within OneDrive.
If the desktop version of Office is already installed on the computer in use, there is an option to Open In … the full version of the software while working on the document.