HTML should be doable.
Depending on the pages there are two ways to ways to do it.
One. Download the file on to the device and load it using the goto or show url
The easiest way however, I think, might be to load it using ajax load, save it into local storage then display it in an html widget. This would depend on the file though. Images and other external files may complicate the process.
I am assuming you are doing this as you want to be able to update the external files and redownload them to the device?