Cannot find bookmarks from OpenXML appended document - vb.net

Question

using the following code snippet I open a document template (DOTX) and then append another document. Both have bookmarks.
Dim m_word As WordprocessingDocument = = WordprocessingDocument.Open("FrontPage.dotx", True)
Dim altChunkId As String = "ChunkId1"
Dim mainPart As MainDocumentPart = m_word.MainDocumentPart
Dim chunk As AlternativeFormatImportPart = mainPart.AddAlternativeFormatImportPart(
DocumentFormat.OpenXml.Packaging.AlternativeFormatImportPartType.WordprocessingML, altChunkId)
Using fileStream As IO.FileStream = IO.File.Open("Appendix.dotx", IO.FileMode.Open)
chunk.FeedData(fileStream)
End Using
Dim altChunk As AltChunk = New DocumentFormat.OpenXml.Wordprocessing.AltChunk()
altChunk.Id = altChunkId
mainPart.Document.Body.InsertAfter(altChunk, mainPart.Document.Body.Elements(Of DocumentFormat.OpenXml.Wordprocessing.Paragraph).Last())
mainPart.Document.Save()
Now if I try to loop trough all bookmarks like this:
Dim docbody As Body = doc.GetFirstChild(Of Body)()
For Each bookmarkStart As BookmarkStart In docbody.Descendants(Of BookmarkStart)()
' Do something with the bookmarks
Next
I only get the bookmarks of the original frontpage.dotx, none of the bookmarks of the appendix.dotx is found.
If I save the document to a file, all the bookmarks are there when I open it using Word. I can also reopen the saved file i C# and then all bookmarks can be found using the above For Each loop. The question is, how can I get all the bookmarks after appending without saving and reloading the document?

Answer 1

When you use AltChunk to embed a document the entire file is embedded into the document - it's NOT integrated. That only happens when the combined document is opened by Word. If you need to work through all the bookmarks you need to either
Open each document, do the bookmarks, and THEN combine the two using AltChunk OR
Not use AltChunk to combine the documents, and transfer the second document part-by-part into the first document.