DOCX Merge corrupting output file

Hi,
Can you check and see if the individual documents (before the merge) are able to be opened? The merge plugin may not be corrupting the output. Instead, the XML of one of the templates may not be created correctly and it will be easier to track down once you know which document is causing it.

I tried opening individual files. they are opening fine.

Is there a requirement to merge the documents, and for them to stay as DOCX? If this is a problem that can't be solved, you may have a few workaround options:
1) Don't merge
2) Convert to PDF and Merge

Is there a requirement to merge the documents, and for them to stay as DOCX? If this is a problem that can't be solved, you may have a few workaround options:
1) Don't merge
2) Convert to PDF and Merge