I just mean the url to the swf file. If you read the flexpaper documentation it tells you to convert your pdf files to swf files using a tool like swftools. After you do that you will need to upload the swf file to your server and place the url to the swf between the short code(eg. http://yourdomain.com/wp-content/uploads/2010/12/thefile.swf). I used the wordpress media manager to upload the files and then just copied the ‘file url’ from the media manager in my testing.