No upload form. Start with the EPUBCheck log only; do not send a full manuscript.

Not an EPUB: DOCX / Office package renamed as .epub

Plain English meaning

Sometimes EPUBCheck errors such as missing mimetype and missing META-INF/container.xml mean the file is not really an EPUB at all. It may be a DOCX or another Office-style ZIP package that was renamed or exported incorrectly.

Why it happens

The wrong file was uploaded to EPUBCheck.
A DOCX was renamed from .docx to .epub.
A conversion/export step failed before creating a real EPUB package.

What you can check yourself

Make a copy of the file.
Rename the copy to .zip.
If you see folders like word/, docProps/, or _rels/, that is likely an Office document package, not an EPUB.
A real EPUB should have mimetype and META-INF/container.xml.

What can usually be fixed

This is usually not a small EPUB repair. The safer fix is to go back to the source document or book tool and export a fresh EPUB.

What cannot be promised

A renamed DOCX cannot be made into a valid EPUB by changing the extension. It must be converted or exported properly. Layout, styles, images, and navigation may need separate formatting work.