Contact
Quickest first. The first two do not need us at all.
Managing your plan
You do not need us for this. Open your account to switch plan, update your details or read past invoices.
Something is broken, or you want it to do something it does not
Put it on the feedback board. It is public and needs no account, so you can see what other people have already asked for and add your vote to it instead of writing the same thing again. That is the list new work is picked from.
Everything else
Email . Billing questions, something about your own account, a document that came out wrong, press, or anything that does not fit above. It goes to one inbox and a person reads it.
If it is about a document that came out wrong, say what you put in (a PDF, a Word file, a link, or a topic) and roughly how long it was. That is usually enough to reproduce it.
Where your documents live
Short answer: on your own device unless you asked otherwise. The long answer is in the privacy policy, and what we owe each other is in the terms.