For juniors: any time you send something important to your manager, confirm they read the document. Don't ask "did you read it?" Don't rely on reactions in chat. Ask a specific question that would require them to read the contents of the document. For example, if you're sending over a quote from a vendor, and you'd already sent another quote before, you could ask "how does this quote compare to the previous one? [link to previous one]" Always get confirmation at least 24-48 hours in advance of the point-of-no-return (e.g. launch, meeting, changing dates, company-wide emails), very preferably in writing.

And for _very_ important meetings, ensure all parties have either acknowledged understanding of the required information, or schedule pre-meeting briefings with individuals. There's nothing quite like getting thrown under the bus because someone showed up and couldn't figure out the subtleties & context on the fly. Unfortunately you can't just say "it's a 12 page document for a reason." when your manager is confused in front of their manager.