Convert string to HttpPostedFileBase
===

I am trying to do upload attachment functionality using MVC. My method that is actually doing the upload/save attachment is expecting a HttpPostedFileBase type.

    public virtual string Upload(HttpPostedFileBase fileName) 
    {
         //Code to upload/save attachment.
    }

My problem is "fileName" is being passed from the UI as a string. How can I convert the string(file path name) into something my Upload method can work with.

Thanks in advance.