Create activity step and in the Implementation->Type (set this as referenced process)
Check the “Allow this step to dynamically invoke one or more referenced processes at run time:” property to true
Generate the process, in the PRESUB_ name service do the mapping
a. set ‘WaitForSubprocess’ as true (in case of synchronous)
b. set ‘SubprocessModelID’ to name of the referenced process to be invoked (‘Project/Process’)
c. set ‘ReturnDocuments’ to the ‘document name’ that gets published in the referenced process (fullpath)
d. set ‘SubprocessInstances/Type’ to the ‘document name’ that is being received in the referenced process (fullpath)
e. Map ‘SubprocessInstances/Document’ to the document that is being received in the referenced process
In case of asynchronous, the ‘WaitForSubprocess’ can be set as false and step c can be ignored
Reference:8-0-SP1_Administering_Process_Engine.pdf