Word found unreadable content in xxx.docx after split a docx using openxml - ms-word

Question

I have a full.docx which includes two math questions, the docx embeds some pictures and MathType equation (oleobject), I split the doc according to this, get two files (first.docx, second.docx) , first.docx works fine, the second.docx, however, pops up a warning dialog when I try to open it:
"Word found unreadable content in second.docx. Do you want to recover the contents of this document? If you trust the source of this document, click Yes."
After click "Yes", the doc can be opened, the content is also correct, I want to know what is wrong with the second.docx? I have checked it with "Open xml sdk 2.5 productivity tool", but found no reason. Very appreciated for any help. Thanks.
The three files have been uploaded to here.
Show some code:
byte[] templateBytes = System.IO.File.ReadAllBytes(TEMPLATE_YANG_FILE);
using (MemoryStream templateStream = new MemoryStream())
{
templateStream.Write(templateBytes, 0, (int)templateBytes.Length);
string guidStr = Guid.NewGuid().ToString();
using (WordprocessingDocument document = WordprocessingDocument.Open(templateStream, true))
{
document.ChangeDocumentType(DocumentFormat.OpenXml.WordprocessingDocumentType.Document);
MainDocumentPart mainPart = document.MainDocumentPart;
mainPart.Document = new Document();
Body bd = new Body();
foreach (DocumentFormat.OpenXml.Wordprocessing.Paragraph clonedParagrph in lst)
{
bd.AppendChild<DocumentFormat.OpenXml.Wordprocessing.Paragraph>(clonedParagrph);
clonedParagrph.Descendants<Blip>().ToList().ForEach(blip =>
{
var newRelation = document.CopyImage(blip.Embed, this.wordDocument);
blip.Embed = newRelation;
});
clonedParagrph.Descendants<DocumentFormat.OpenXml.Vml.ImageData>().ToList().ForEach(imageData =>
{
var newRelation = document.CopyImage(imageData.RelationshipId, this.wordDocument);
imageData.RelationshipId = newRelation;
});
}
mainPart.Document.Body = bd;
mainPart.Document.Save();
}
string subDocFile = System.IO.Path.Combine(this.outDir, guidStr + ".docx");
this.subWordFileLst.Add(subDocFile);
File.WriteAllBytes(subDocFile, templateStream.ToArray());
}
the lst contains Paragraph cloned from original docx using:
(DocumentFormat.OpenXml.Wordprocessing.Paragraph)p.Clone();

Answer 1

Using productivity tool, found oleobjectx.bin not copied, so I add below code after copy Blip and ImageData:
clonedParagrph.Descendants<OleObject>().ToList().ForEach(ole =>
{
var newRelation = document.CopyOleObject(ole.Id, this.wordDocument);
ole.Id = newRelation;
});
Solved the issue.