# EPUBCheck PKG-003: Unable to read EPUB file header. This…

Source: https://epublab.com/epubcheck/pkg-003/ (updated 2026-11-03)

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.

- 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.

## How to fix it

- Download or export the EPUB again and compare its size with the original.
- Rename a copy to .zip and try to open it: if no ZIP tool can, the file has to be rebuilt from its source.

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