I am thinking on this approach
1) You must be submitting the documents in some table on DB1
2) Add extra fields to store the DB server details where the document is coming from (other applications)
3) Write task in DB1 server to add remote server in DB1
Read here about remote server and why we need it
View or Configure Remote Server Connection Options (SQL Server) | Microsoft Docs[
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4) Add trigger in DB1 document table to look for newly accepted document and then accordingly run the CRUD operations on other database using the remote server connection