Ask HN: How do you securely exchange files with others in your life?

So lets say you're texting with your parents about their finances or your partner or real estate agent about an upcoming purchase - specifically someone less technically inclined. They need to send you some spreadsheets or PDFs that contain information best kept secure - what methods, services, or applications do you tell them to use? What if the tables are turned and you are sending them something?

Is there a gap between best practice and the reality of what usually ends up happening, and if so, why do you think that is?