You need to change node owner to the new docment.
Refer to API
http://www.doc.ic.ac.uk/~sjn5/xml-tr2/docs/api/index.html Steps
1. Read origienal document to which you want to appent node.
2. Read xml document, elements from which are to be appended to the document in step 1 above. Find element to be appended to the document in step 1 above
3. Using document object in step 1 change node owner of the node
e.g. xmlDoc.changeNodeOwner(docElement);
4. Now add node in step 3 to element from document in step1
Regards
Anup