Yeah, PDF didn't anticipate streaming. That pesky trailer dictionary at the end means you have to wait for the file to fully load to parse it.
Having said that, I believe there are "streamable" PDF's where there is enough info up front to render the first page (but only the first page).
(But I have been out of the PDF loop for over a decade now so keep that in mind.)
Yes, you're right there are Linearized PDFs which are organized to enable parsing and display of the first page(s) without having to download the full file. I skipped those from the summary for now because they have a whole chunk of an appendix to themselves.
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.