[Wendy Cutler]

...
The companion contains no data or files...

And Jeffn1 said "When you back up from the tablet into the Companion, it create an MS database file on your computer. "

Thank you for your replies.

What has me confused is that when I opened Companion and then attached the tablet, it did transfer 857088 bytes to a file on the pc. There does seem to be a file - as I said, it showed me the filename, hence the question about whether it is just a temporary file or what.
So if I do a backup, is that another copy of the same file? I have not tried backup from Companion - does it save the backup to the Companion directory, so does not use Dropbox space?