Hi Dan,
Each document is a separate database so there is no way to grab data from other documents within the same account.
We recommend keeping all similar data in the same document. You could put everything into the same document that includes a page that lists all client contact information, then add a client column to all other data assign each record to the appropriate client. You can set up access rules so each client only sees their own information when they access the document. There’s a great video example of this below:
The post linked below has a good explanation of why we recommend this setup: