# PKG-003: unreadable EPUB file header, how to fix it

Source: https://epubcc.com/epubcheck/pkg-003/ (updated 2026-11-04)

EPUBCheck PKG-003 is an error message: “Unable to read EPUB file header. This is likely a corrupted EPUB file.” EPUBCheck could not read the start of the file as a ZIP archive, so it is not a usable EPUB. Every EPUB is a ZIP container, and reading apps and stores reject a file whose header is not a valid ZIP header.

- Official message (EPUBCheck 5.4.0): Unable to read EPUB file header.  This is likely a corrupted EPUB file.
- Default severity: Error

## Typical causes

- The file is not really an EPUB: a PDF, MOBI or other file renamed to .epub.
- The download or copy was cut short and the file is truncated.
- An HTML error page or a login page was saved with the .epub name instead of the book.

## How to fix it

1. Download or export the EPUB again and compare its size with the original.
2. Rename a copy to .zip and try to open it: if no ZIP tool can, the file has to be rebuilt from its source.
3. If the file is another format renamed to .epub, convert it properly instead of renaming it.
4. Run EPUBCheck again on the rebuilt file and fix any message that appears next: a damaged archive can hide other problems until it can be read.

## When it's not this

If the ZIP opens but its directory is damaged, EPUBCheck reports PKG-004; if the path itself is wrong, PKG-018.

## Sources

- EPUB 3.3, §4.3.2 ZIP file requirements: https://www.w3.org/TR/epub-33/#sec-zip-container-zipreqs (read 2026-11-04)

Message text and severity: EPUBCheck (W3C, BSD-3-Clause). Explanation: EpubCC.