1. Yes, file transfer is entirely possible through USB, that’s mainly how I use it
2. No, since a restructuring in subscription tiers the conversion feature is available as long as you are online and have an account with them that you are logged into.
3. You can upload pdfs to the device and you can take notes over them so yes, annotating/filling documents is possible. Uploading templates is technically possible but not supported out of the box, you have to dig a bit for that.