Although you can add and edit Documents and Media files via upload and download, Liferay DXP doesn’t contain a UI that lets you author or edit documents directly. You can, however, create and edit Documents and Media files online in Word™, Excel™, and PowerPoint™.
Note that when you use Office 365™ to create or edit a Documents and Media file, that file isn’t permanently stored in Office 365™. Office 365™ is only used for its editing UI. Your edits are then saved to the Documents and Media Library.
Here you can learn how to use it.