http://www.rfc-editor.org/rfc/rfc8118.txt
RFC 8118: The application/pdf Media Type, M. Hardy, L. Masinter, D. Markovic, D. Johnson, M. Bailey2017-03-01T23:00:00-00:00The Portable Document Format (PDF) is an ISO standard (ISO 32000-1:2008) defining a final-form document representation language in use for document exchange, including on the Internet, since 1993. This document provides an overview of the PDF format and updates the media type registration of "application/pdf". It obsoletes RFC 3778.