Steps to Reproduce:
- Go to https://en.wikipedia.org/wiki/Rail_transport_modelling
- Press "Download as PDF" in the left menu
- Press "Download"
Note: I am able to reproduce this with Lewis_Hamilton at enwiki as well, as well as Funkcionalismus at cswiki. It doesn't seem to be a single wiki/page issue.
A PDF file is downloaded to your computer, but opening it via Firefox's internal viewer, Chrome's internal viewer, or Adobe Acrobat tells me it is invalid.
The Download as PDF feature gives me a valid PDF that contains the article itself.
This may or may not be related to T266373: Connection closed while downloading PDF of articles, which is said to be relevant at wikis with Desktop Improvements project installed. Given the files differ in size:
it might be a symptom of the task mentioned?
Example invalid PDFs: