Just fyi to cheapskates like me, i was looking around for a free pdf, some are hosted on github, others on google docs. Putting the pdf urls into https://www.virustotal.com/gui/home/url , all were suspicious or malicious. I think ill search around a bit more, but will probably give up.
Unfortunately it seems pdfs linked there may also be malicious ( https://www.virustotal.com/gui/url/7e73cc3d685c77d88ad9cf769... ). I checked on some other pdf links ive downloaded previously and they were safe, so I don’t believe the software just flags everything.
But it could be if the coding book includes working examples and exercises, that would probably flag any system looking for code execution.