Embedded Documents in MS Word

Recently I had trouble opening PDF documents embedded in Microsoft Word. I speculated about the following reasons for this problem:

1. Adobe Acrobat not installed, I use MuPDF
2. Embedded document simply not "really" embedded but just an icon

There is an easy solution. Microsoft Word 2007 documents are just zip-files. Just look at output of

7z l WordDocument.docx

The folder word/embeddings contains the embedded files, regardless of its type.

By the way, LibreOffice/OpenOffice files are also just zip-files.