Uploading a 1MB PDF I'm getting « upload is too big, maximum is 4MB »

I’m getting a 413 Request Entity Too Large from nginx so clearly I have to dig further to understand why a “big” image is OK but a “not so big” PDF is not…

The 3.0MB JPG have a Content-Length of  557215 so 0.5MB surprisingly!
The 2.3MB PDF have a Content-Length of 2460137 so 2.3MB unsurprisingly.

Does Discourse rescale the jpg before uploading it?

On my passing JPEGs I see the image width and height as different after uploading them to Discourse (Tried with https://apod.nasa.gov/apod/image/2209/DSCF4968_PS_Lioce.jpg, it’s a 5703x3892, 3.6MB picture, but once uploaded it’s a 1920×1310 of 153 KB one.