Streaming with a footer should still be possible if your website is capable of processing range requests and sets the content length header. A streaming PDF reader can start with a HEAD request, send a second request for the last few hundred bytes to get the pointers and another request to get the tables, and then continue parsing the rest as normal.

Not great for PDFs generated at request time, but any file stored on a competent web server made after 2000 should permit streaming with only 1-2 RTT of additional overhead.

Unfortunately, nobody seems to care for file type specific streaming parsers using ranged requests, but I don't believe there's a strong technical boundary with footers.