@craigmcclellan I know that GitHub "raw" files are served with a Content-Type header of text/plain, so Safari won't know it's a PDF (until fully downloaded at least). I can't say why they do that.
Replying to:

@craigmcclellan I know that GitHub "raw" files are served with a Content-Type header of text/plain, so Safari won't know it's a PDF (until fully downloaded at least). I can't say why they do that.