After trying to create document placeholder from campaign object as Record action 

using below code then I am trying to update document Owner Role but I am unable to get document versionId.. though I am getting it as String but I want it as DocumentVersion. How can I get that?

SaveDocumentVersionsResponse documents = 
        documentService.createDocuments(VaultCollections.asList(r));

String documentVersionId = documents.getSuccesses().get(0).getDocumentVersionId();

DocumentRoleService docRoleService = ServiceLocator.locate(DocumentRoleService.class);
String ROLE_TO_CHECK = "owner__v";

DocumentRoleUpdate docRoleUpdate = docRoleService.newDocumentRoleUpdate(ROLE_TO_CHECK, documentVersionId);
// documentversion id is string but it should be of Type DocumentVerison How to get that?

docRoleUpdate.addUsers(VaultCollections.asList(docOnwerId));

//Add up to 500 role updates in a single batch
docRoleService.batchUpdateDocumentRoles(VaultCollections.asList(docRoleUpdate))
.rollbackOnErrors()
.execute();