RSC-004 is reported as info by default. Informative only. It does not make the EPUB invalid.

EPUBCheck · Resources and references

EPUBCheck RSC-004: encrypted file not checked

Updated: Nov 4, 2026

EPUBCheck RSC-004 is an info message: “File "…" is encrypted, its content will not be checked.” A file is encrypted (listed in META-INF/encryption.xml), so EPUBCheck cannot read it and skips its checks. It is an informative message, not an error.

The official message

File "%1$s" is encrypted, its content will not be checked.

Default severity: Info. Informative only. It does not make the EPUB invalid.
EPUBCheck version: 5.4.0

%1$s, %2$s… are filled in with the file, value or element EPUBCheck found.

Typical causes

Books protected with DRM, where content files are encrypted with a method EPUBCheck cannot read.
A store or distributor copy of the book rather than the original file.

How to fix it

Nothing to fix if the encryption is intended.
To check the content, validate the unencrypted source EPUB you produced, before DRM was applied.
Never try to remove DRM from a book you do not have the right to modify.

When it's not this

Font obfuscation listed for a non-font file is a different problem, PKG-026.

Terms used here

Other RSC messages

RSC-003 No rootfile tag with media type "application/oebps-package+xml" was found in the container.
RSC-005 Error while parsing file: …
RSC-002 Required META-INF/container.xml resource could not be found.
RSC-006 Remote resource reference is not allowed in this context; resource "…" must be located in the EPUB container.
RSC-006b Resource "…" is located outside the EPUB Container; please check the resource is retrieved in scripted content.
RSC-001 File "…" could not be found.

Sources

EPUB 3.3, §4.2.6.3.2 Encryption file (encryption.xml) · read Nov 4, 2026

Message text and severity from EPUBCheck 5.4.0 (W3C, BSD-3-Clause). Explanation by EpubCC.