Multiple users can edit a single Office 365 document at one time. You can share editing with both Etown network users, and non-Etown network users. First navigate to “portal.office.com” in a web browser such as Google Chrome. Open the document you want to share and click the share button in the top right.
Next, type in the email of the user you would like to share with. Include a message describing the document and what you intend for them to edit. Make sure the drop down box is set to “can edit.” Although, you can also share a document set to “can view” to allow users to read, but not edit, the document.
The user will receive an email alerting them you shared a document and providing a link to the document. All Etown network users have access to Office 365, but a non-Etown network user will have to sign in or create a Microsoft Account to view or edit the document.
Link to Knowledgebase article: http://helpdesk.etown.edu/helpconsole2012/KB/default.aspx?pageid=multiple_user_editing