Once on July 4 and July 9 and several times today (July 11) I'm seeing file requests (pdf files) from what is to me a new Fecebook IP subnet - 57.141.5.0/24. No previous activity seen going back 5+ years from 57.141.0.0/16. This is technically assigned to Meta Platforms Ireland.

No referrer, no robots.txt. User-agent was:

facebookexternalhit/1.1 (+http://www.facebook.com/externalhit_uatext.php)

Can someone connect the dots for me, complete the circle, show me what the end-use is for FB in grabbing these files?

How does it feed back into some sort of human interaction with FB?

I rarely interact with FB, I only do so to find rare car parts, I don't use FB as a general web search portal - does it even have that capability?

What is the economic or business or platform use-case for FB to be requesting these files?