fsharp.org/specs PDF links show as garbage

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:

```sh
🐚$ 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