I have two file Geo-databases with attachments, relationship classes etc. but both database schema's are same. I want to merge them into one file Geo-database with attachments, relationship classes etc. How can I merge them in arcgis?
Use the Append tool. Starting at 10.5 there is an environment setting 'Maintain Attachments' that will also append the attachments. You will want to run this tool for the feature class and related table.