Your S3 setup appears to send no CORS headers currently for any of the PDF documents. This means we have to use a conduit/proxy server to get your PDFs before presenting them to our users.
It would be great if you could allow access from all origins on the S3 document URLs, as it is rather wasteful in terms of bandwidth to download them twice (once from your server to ours, and then from our server to our users). Better still, make your URLs static - I mean, why go to the trouble of using pre-signed URLs for data that is essentially public anyway?
Details on how to set up CORS for S3 are available here: https://docs.aws.amazon.com/AmazonS3/latest/dev/cors.html
Thanks very much and have a great week ahead
Dev Team @ OSREC Tech