That's correct, we're not suggesting people use Chrome on their iOS device (but is a good question and a super common bit of feedback we got doing training for this stuff with end-users, who assumed that's what we meant). The subtext for the Chrome recommendation is "that's the browser you use on your general-purpose computer". WebKit on iOS benefits (imperfectly, but vs. a general-purpose machine it's probably a wash) from iOS's built-in application sandboxing and security controls.
Regarding sharing of sensitive documents: if you have to do it over the Internet, use a secure messenger to do it. Email attachments are probably the second most dangerous attack vector facing end-users (after phishing). That's why we tell people to use Google Mail; attachments open in their browser viewer and are rendered Google-serverside.
You don't need to convince everyone to use Signal; it's adequate to use WhatsApp, which, again, is already one of the most popular messaging applications in the world (this is one of the reasons getting Signal Protocol baked into WhatsApp was such a monumental achievement).
Regarding sharing of sensitive documents: if you have to do it over the Internet, use a secure messenger to do it. Email attachments are probably the second most dangerous attack vector facing end-users (after phishing). That's why we tell people to use Google Mail; attachments open in their browser viewer and are rendered Google-serverside.
You don't need to convince everyone to use Signal; it's adequate to use WhatsApp, which, again, is already one of the most popular messaging applications in the world (this is one of the reasons getting Signal Protocol baked into WhatsApp was such a monumental achievement).