You can manually upload files, they just need to be served by a web server. As long as they are on a web server that’s fine. If you are opening the files locally it is not. Unfortunately, there are a whole lot of limitations of the file:// protocol that simply aren’t easy or practical to work around.
As far as exporting the files you have selected, I am not sure I understand the problem. If you only select a few files to export it will only export the ones you have selected.
