: The file is not recognized as a proper ZIP-based EPUB.

: The file is protected by Digital Rights Management and cannot be opened on unauthorized devices.

: The EPUB (Electronic Publication) format itself is the global standard for reflowable digital books, supported by almost all major e-readers and apps like Apple Books and Google Play Books .

If you are seeing "5190" in a specific app, could you clarify is displaying it? This will help pinpoint if it's a specific library ID or a localized system error.

: While there is no standard "Error 5190" for EPUB files, similar four-digit codes often appear in specific proprietary systems or during file validation (e.g., using EPUBCheck ). Common issues that cause such errors include:

: Issues within the content.opf file that prevent the e-reader from understanding the book's structure.