system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: My boss sends me PDF through company email about a vendor he's considering. Next day, said vendor's ads are showing up in my FB newsfeed. How did they know?

How can FB tell what PDF's I'm opening or email I'm reading? Our company uses Exchange and Outlook. I use Chrome and FF for browsers.
gpt
If you have your workplace listed in your Facebook profile they can target you with their ads. If they have a bid in with your company they could be trying to stealthily get their name in your subconscious by targeting employees of your company.