Hello Martin Chamorro,
The built-in WebEditor does not support setting default folder or setting permissions over a folder. You will need a custom selector that lists only certain directory from your file system from where you can select/upload files. You can expose a property in your custom selector from where you can set the path which should be used by the selector. You can bind the file system files to RadGrid control.
All the best,
the Telerik team
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