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PKG-006: mimetype missing, compressed, or not first

Plain English meaning

An EPUB is a ZIP package with a special rule: the first file in the ZIP must be named mimetype, it must contain application/epub+zip, and it must be stored uncompressed.

If EPUBCheck reports PKG-006, your EPUB package is missing that rule or the file is in the wrong place.

Why it happens

• The EPUB was zipped manually in the wrong order.
• The mimetype file was compressed.
• The file was exported by one tool and repacked by another.
• The file extension says .epub, but the package is not actually an EPUB.

What you can check yourself

1. Make a copy of the EPUB.
2. Rename the copy from .epub to .zip.
3. Open the ZIP and check whether a file named mimetype exists at the top level.
4. Open it with a text editor and confirm it says application/epub+zip.

What can usually be fixed

If the rest of the EPUB package is valid, this is often a small repackaging fix: put mimetype first, store it without compression, then add the rest of the files.

What cannot be promised

If the package is actually a DOCX / Office file, a random ZIP, or an incomplete export, there may be no EPUB to repair. In that case the right answer is usually to export a fresh EPUB from the source tool.