Ebook conversions go wrong in predictable ways. Whether a file will not open, a layout collapses, or the output is full of gibberish, the cause is almost always the same handful of issues. This is the field guide to the ten most common ebook format problems and the fix for each — plus how to avoid them in the first place.
1. EPUB Won't Open on a Kindle
Kindles do not read EPUB. Send an .epub and the device rejects it. Fix: convert to AZW3 first with EPUB to AZW3, or email it through Send to Kindle so Amazon converts it. If the book will not open on any reader, see 5 reasons your ebook won't open on Kindle.
2. MOBI Looks Broken After Conversion
MOBI is a legacy format with weak CSS support, so a conversion into MOBI flattens fonts and tables. Fix: target AZW3 instead of MOBI for modern Kindles. If your source is already MOBI and you want it portable, convert MOBI to EPUB to restore reflow.
3. PDF Converts but Loses All Formatting
PDF is a fixed-page format; turning it into a reflowable ebook means the converter has to reconstruct the structure. Fix: use a formatting-aware path. Convert PDF to EPUB without losing layout explains the settings; the tool itself is PDF to EPUB.
4. Tables and Images Disappear
Some formats (notably MOBI and a bad PDF extraction) drop tables and images. Fix: keep the source in EPUB or AZW3, which preserve both, and avoid converting through MOBI. For EPUB output, EPUB to PDF keeps images if the source has them.
5. Chapter Headings Don't Show Up
A missing table of contents usually means the source had no proper heading structure. Fix: ensure the source uses real headings (H1/H2), not big bold text. Converters build the TOC from headings, so fixing the source fixes the navigation.
6. Embedded Fonts Get Dropped
MOBI and some PDF paths strip embedded fonts. Fix: convert to EPUB or AZW3, which carry embedded fonts. If a specific font matters, keep it in the source and target a format that supports it.
7. The File Is Too Large to Upload
Image-heavy EPUBs or scanned PDFs can exceed upload limits. Fix: shrink images first, or split a massive PDF. Most browser converters cap a single file; reducing image resolution usually gets you under the limit without hurting readability.
8. Conversion Fails or Times Out
A failed conversion often means a corrupt source or an unsupported feature. Fix: open the file on your computer to confirm it is intact, then retry. For many files at once, use batch conversion instead of one giant upload.
9. The Download Link Expires
Some services expire the download after a few minutes. Fix: download as soon as the job finishes. BookConv lets you download directly from the result page; save the file before moving on.
10. Strange Characters or Gibberish in the Output
Gibberish (mojibake) means an encoding mismatch, common with older TXT or non-UTF-8 sources. Fix: re-save the source as UTF-8, then convert. For plain text, TXT to EPUB builds a clean ebook with a proper TOC.
Build a Clean Source File First
Most of these problems trace back to the source, not the converter. Before converting:
- Use real headings so the TOC builds correctly.
- Keep images at a reasonable resolution to stay under upload limits.
- Save text sources as UTF-8 to avoid gibberish.
- Prefer EPUB or AZW3 as the target so fonts and tables survive.
Our pre-conversion checklist walks through each step.
Key Takeaways
- Most failures start in the source — fix headings, encoding, and image size first.
- Target EPUB or AZW3, not MOBI, to keep fonts, tables, and TOC.
- PDF needs a formatting-aware path to avoid layout loss.
- Kindle needs AZW3, never raw EPUB.
- Prepare the file with the pre-conversion checklist and most problems never appear.