Ideally I would try to put another docx to a docx. I tried using a html file as posted in other forum.

I tried to do below steps:
1. I created a very small docx file with 2/3 lines written using MSWord.
2. Save it.
3.Open the docx using xmlSpy.
4. Add a html file under /word.
5. Edit Contents.xml to have the new content type.  <Default Extension="htm" ContentType="application/html"/>
6.Edit .rels file to include unique relationship
<Relationship Id="rId1000" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/aFChunk" Target="word/xxx.htm"/>
7.Edit document.xml and add <w:altChunk r:id="rId1000"/> inside body node.
8.Save the docx.

Open the docx file and error in opening. I redo it. This time till step 4 and it does show "error in opening" error. Addition of a new part in the zipped package is not working at all in this straight way. Forget about any xml tag error.

Can anybody throw an idea?

Thank you.