Hi !
I think that is not a easy way to do it.
Solution that i found is to get the file content in something like this:
SS 1.0:
var file= nlapiLoadFile(File_ID);
data_file= { "file": file.getURL(), "name": file.getName(), "type": file.getType(), "content": file.getValue() };
SS 2.0
var file_= file.load({
id: file_id
});