みんなありがとう!
ここに私の最終的な作業コードがあります:
' Copy XML parts to define document
NewDocument.AddPart(templatedoc.GetPartById("rId3"), "rId3")
NewDocument.AddPart(templatedoc.GetPartById("rId2"), "rId2")
'// Add a main document part.
Dim mainPart = NewDocument.AddMainDocumentPart()
' // Add a Body
mainPart.Document = New Document(New Body())
'Copy Document XMLParts - must be in specific order
mainPart.AddPart(templatedoc.MainDocumentPart.GetPartById("rId8"), "rId8")
mainPart.AddPart(templatedoc.MainDocumentPart.GetPartById("rId3"), "rId3")
mainPart.AddPart(templatedoc.MainDocumentPart.GetPartById("rId7"), "rId7")
mainPart.AddPart(templatedoc.MainDocumentPart.GetPartById("rId2"), "rId2")
mainPart.AddPart(templatedoc.MainDocumentPart.GetPartById("rId1"), "rId1")
mainPart.AddPart(templatedoc.MainDocumentPart.GetPartById("rId6"), "rId6")
mainPart.AddPart(templatedoc.MainDocumentPart.GetPartById("rId5"), "rId5")
mainPart.AddPart(templatedoc.MainDocumentPart.GetPartById("rId4"), "rId4")
mainPart.AddPart(templatedoc.MainDocumentPart.GetPartById("rId9"), "rId9")
'// Copy text from template document
Dim containerElement = NewDocument.MainDocumentPart.Document.Descendants().FirstOrDefault()
Dim clonedElements = New List(Of OpenXmlElement)
Dim elementstocopy = templatedoc.MainDocumentPart.Document.Body.ChildElements
For Each element As OpenXmlElement In elementstocopy
clonedElements.Add(element.Clone())
Next
containerElement.RemoveAllChildren()
containerElement.Append(clonedElements)
mainPart.Document.Save()