fsharp.org/specs PDF links show as garbage

[mikesamuel]

When I go to the website, https://fsharp.org/specs/language-spec/ , I click on the PDF links and I get the below.
I expected to open in the browser's builtin PDF viewer.
I'm using Chrome Version 142.0.7444.176 (Official Build) (x86_64).

Website:

Clicked on link ( https://fsharp.org/specs/language-spec/4.1/FSharpSpec-4.1-latest.pdf ):

If I try to curl that same URL, I get a sensible looking content-type header:

🐚$ curl -I 'https://fsharp.org/specs/language-spec/4.1/FSharpSpec-4.1-latest.pdf'
HTTP/2 200
server: GitHub.com
content-type: application/pdf

Nothing about the other headers looks terrible, but I notice there's no content-disposition: attachment; filename="FSharpSpec-4.1-latest.pdf". But my HTTP header knowledge is rusty.

other headers

last-modified: Wed, 12 Nov 2025 22:47:41 GMT
access-control-allow-origin: *
etag: "69150e8d-3c9e0d"
expires: Fri, 12 Dec 2025 15:58:34 GMT
cache-control: max-age=600
x-proxy-cache: MISS
x-github-request-id: 18DC:1B46:2F554A:334A5A:693C3952
accept-ranges: bytes
age: 264
date: Fri, 12 Dec 2025 15:52:58 GMT
via: 1.1 varnish
x-served-by: cache-den-kden1300050-DEN
x-cache: HIT
x-cache-hits: 0
x-timer: S1765554778.089245,VS0,VE1
vary: Accept-Encoding
x-fastly-request-id: 3d9ada5a4f2d57bb6f2bdc0d08a0afcba2c97faa
content-length: 3972621

[mikesamuel]

If I curl the file I get a well-formed PDF.

🐚$ curl 'https://fsharp.org/specs/language-spec/4.1/FSharpSpec-4.1-latest.pdf' > ~/Documents/FSharpSpec-4.1-latest.pdf
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 3879k  100 3879k    0     0  3031k      0  0:00:01  0:00:01 --:--:-- 3030k

[mikesamuel]

Note, the oldest version on that site is F# 4.1, but iirc, F# 9 is modern.

[mikesamuel]

Maybe that whole page has been superseded by https://fsharp.github.io/fslang-spec/ and is only of historical interest.