Thank you for the provided detail information.
As I mentioned in my previous answer, when a file is opened by the browser, the displayed file is not the actual file that resides on the server but a downloaded copy. This is not a restriction of RadFileExplorer but is the standard concept - users do not have direct access to the files, they are served by the web server.
In order to achieve the required functionality, I would recommend to instruct the users to download the files, modify them and then upload the files back. In the following live demo you can find an example of how to force file download:
Filter files and download
the Telerik team
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