The documents stored on the cloud, such as in your Microsoft OneDrive, Google Drive or Dropbox accounts, need to be downloaded so as to edit them. Then after updating, you must re-upload them with the same name (overwritten in that case) or different name (to maintain different versions of the documents). They cannot be edited live, in real time.
However, there is an alternative way of updating your cloud documents without downloading and uploading them. Instead of adding documents in CORE, you can add the links to those actual documents on your cloud storage account. Every time you click the links, it opens the latest version of the documents. Cloud storage solutions such as Google Drive, Dropbox or OneDrive maintain the history of each version as it is. In this case, the cloud storage provider specified in CORE > Global Settings does not matter. You need to specify an 'edit' link URLs in CORE or share the documents with specific users to provide Edit access. Both these functions need to be done in your cloud storage software and not in CORE. Check CORE Help Center for details.