If I make updates to a file, document or note (e.g. revision) that is attached to one of my tasks or messages, would it update automatically? Or do I need to reattach?

Azendoo only has the sharing link to this file, document or note.
So as long as this sharing link does not change, Azendoo will always link to the latest version/revision of it.

You can upload revisions of files that are on Google Drive, Dropbox or Box.
Google Drive native documents like docs, spreadsheets or presentations can be updated and co-edited.
The sharing link in Azendoo gives access to the latest revision or current version.

Evernote notes are automatically synched so the sharing link gives access to the current version.