We are considering running 2 separated Alfresco instances, with different documents, and we would like to easily transfer a document from instance B to instance A, in the right folder. Is there an easy way to do this? Also, is there an easy way to have instance B search results available in instance A?
I think you can look at the TransferService and perhaps the Replication Jobs. About your second question, in Alfresco Explorer, it's possible to configure an Opensearch search to another Alfresco instance but I don't think it's possible in Alfresco Share. Perhaps an add-on could do that.