The recipe below the line can now be implemented much easier usign the new (v.1.16.8) cammand line interface of PyMuPDF. Also note that MuPDF does no longer support embedded files since after their version 1.14, so PyMuPDF is unique in that respect. The following command of the fitz module deal with embedded files:

• python -m fitz embed-info - list embedded files (long and short versions)
• python -m fitz embed-add - insert a new file
• python -m fitz embed-del - delete a file
• python -m fitz embed-upd - update a file
• python -m fitz embed-extract - extract data of a file
• python -m fitz embed-copy - copy embedded files between two PDFs

Please see the documentation for details or request help (-h) from the command line.

There also exist example scripts here.