You can use services in wm.tn.query folder.
Use the wm.tn.query:createDocumentQuery and give internal ID of receiver
Then use the wm.tn.query:documentQuery and disable paging. You should be able to see the internal ids. Use the internal id as an input to service getContentPart and you should be able to get the data in pipeline
Else as Mashesh mentioned below. you need to make a join between tables bizdoc and bizdoccontent to identify the rows for a particular receiver
#B2B-Integration#webMethods#Integration-Server-and-ESB