Opening databases in DT3

I have just purchased and installed DT3. My Global inbox opens OK but I am unable to open any of the other databases that I have.
All my databases are in the DEVONthink 2 pro folder. Are they supposed to be copied across to the new database folder or do I move them myself?
I currently use iCloud for syncing and its been fine with DT2 Pro. Do I need to make any changes for it to work with DT3. I use DTTG extensively and rely on the sync to upload any files I’ve added in IOS to appear in DT2 Pro.
Sorry if not doing something which is obvious. Currently I’ve reverted back to using DT2 Pro.
Thanks.

All my databases are in the DEVONthink 2 pro folder.

In Application Support?
This is acceptable but a bit unusual.

Are they supposed to be copied across to the new database folder or do I move them myself?

No they’re not supposed to be copied over, and they don’t have to be moved in this case. However, they can be, if desired.

What do you mean by "I am unable to open any of the other databases "?

Thanks for the very quick response.
My databases are in a folder 'username/DEVONthink Pro Office. DT3 has created a folder 'username/Databases. I can easily copy them into that new folder if required.
Will this have an impact on syncing to iCloud?

You’re welcome.
You can keep them in that folder, if desired.

And no, it has no effect on syncing of any kind.