javascript creating a file from URL

You cannot create a File object only giving an URL to it.

The right method is to get the file through a Http request and read it, with something like this:

var blob = null
var xhr = new XMLHttpRequest()
xhr.open("GET", "path/to/file")
xhr.responseType = "blob"
xhr.onload = function() 
{
    blob = xhr.response
    LoadAndDisplayFile(blob)
}
xhr.send()