Book Checker
Client-side · No upload · No account
Before you install anything, find out whether your actual book will open. Drop in an EPUB, PDF or Kindle file and this page reads its structure — DRM, text layer, form fields, fonts, size — and tells you exactly what will and won't work, including the parts that won't. Everything runs in your browser; the file is never sent anywhere.
Drop an EPUB, PDF or Kindle file here
The file is read in your browser and never leaves your device — no upload, no server, nothing stored.
What it checks
Every check is read from the file itself. Where a format hides something that can't be confirmed without rendering the whole document, the result says so rather than guessing.
- DRM vs. obfuscated fonts — told apart correctly
- EPUB 2 or 3, reflowable or fixed-layout
- Interactive workbook fields that save your answers
- MathML equations and vector diagrams
- Embedded fonts and non-Latin scripts
- Publisher JavaScript and embedded media
- Password and permissions encryption
- Real text layer vs. scanned images
- Fillable AcroForm fields — and unsupported XFA forms
- Page count read from the document index
- MOBI, AZW and AZW3 recognised by their header
- Amazon DRM flag read from the PalmDOC record
- Which study features a Kindle file supports
The three reasons a study book disappoints
DRM. An encrypted book is locked to the shop that sold it. No reader on any platform can open it, and any app that claims otherwise is lying to you. The checker distinguishes real DRM from font obfuscation, which looks identical to most tools and is completely harmless.
No text layer. Scanned handouts and photographed textbooks display beautifully and do nothing else. Without selectable text there is nothing to highlight, look up, search or read aloud — and therefore nothing to turn into highlights and flashcards. OCR fixes this permanently, before you import.
Fixed layout. Pre-paginated books render exactly as the publisher drew them, which is right for a diagram-heavy textbook and wrong if you wanted larger type on a phone. Knowing which one you have before you start reading saves an evening of fighting the settings.
Questions
Does this upload my book anywhere?
No. The file is read in your browser using the same code that renders this page — it is never sent to a server, never stored, and never seen by anyone but you. Turn off your connection after the page loads and the checker still works.
How can it tell whether my EPUB has DRM?
It reads META-INF/encryption.xml and META-INF/rights.xml inside the archive. The important detail most checkers get wrong: an encryption.xml that only lists the IDPF or Adobe font-mangling algorithms means obfuscated fonts, not DRM, and that book opens perfectly. Only other algorithms, or an Adobe rights.xml, mean the file is actually locked.
Why does my scanned PDF fail the text-layer check?
A scan is a stack of photographs. There is no text in it to select, so highlighting, dictionary lookups, search and read-aloud have nothing to work with. The pages still display perfectly. Running the file through OCR — Acrobat, ocrmypdf or most scanner apps — adds a text layer and restores every one of those features.
My book bought from Amazon says Kindle DRM. Can anything open it?
Only Amazon's own apps, on the account that bought it. That is what Kindle DRM is for. Books from DRM-free stores, public-domain sources or your own conversions have no such flag and open in GemReader like any other file.
How big a book can GemReader handle?
Up to 200 MB. Above 50 MB it switches to a chunked import path that verifies a checksum and resumes if the import is interrupted, so large illustrated textbooks import reliably.