Conversion Problem: Embedded OpenType TT fonts in DOCX files

Bug #1921793 reported by Colin
This bug affects 1 person
Affects Status Importance Assigned to Milestone
Fix Released

Bug Description

PROBLEM (100% consistent and reproducible)

When embedding OpenType Layout fonts with TrueType outlines in a Word DOCX file and then converting to EPUB in Calibre, and performing the Edit Book -> Run Check test, it will report font problems due to the spaces in the filenames.

Here's an example of the message in the Calibre editor when embedding Bookman Old Style:

"The filename fonts/Bookman Old Style - Regular.ttf contains unsafe characters, that must be escaped, like this fonts/Bookman%20Old%20Style%20-%20Regular.ttf. This can cause problems with some e-book readers. To be absolutely safe, use only the English alphabet [a-z], the numbers [0-9], underscores and hyphens in your file names. While many other characters are allowed, they may cause problems with some software."

This does not happen with OpenType fonts with PostScript outlines, but only because they are not embeddable.


Confirmed in Calibre 5.14 on Windows 10 H2 (Build 19042.867) on a DOCX generated by Word 16.0.13801.20288.


The automated fix in the Book Editor works perfectly every time, so we know that Calibre already has the full capability to address these proactively at time of conversion: E.g., The link that says, "rename the file fonts/Avrile Sans - Regular.ttf to fonts/Avrile_Sans_-_Regular.ttf."


As part of the conversion process from DOCX to EPUB/AZW3, please convert the font names to exclude spaces in the final names. Convert the spaces to underscores. If there is a reason to avoid doing this, then please provide this as a new conversion option on the DOCX input tab of the Conversion window.


This emerges from what is really more of a Word bug or odd design choice (generates font file names based on font family and style names and not using the font file name, which means users have no control over the embedded font file names), but not something MS is likely to fix anytime soon. Therefore, while the problem is with the DOCX file generation by Word, the only way to fix this lies with Calibre.

Revision history for this message
Colin (granitestatecolin) wrote :
summary: - Embedded OpenType TT fonts - Word adds spaces to font name, need Calibre
- them for full compatibility
+ Conversion Problem: Embedded OpenType TT fonts in DOCX files
description: updated
Revision history for this message
Kovid Goyal (kovid) wrote : Re: calibre bug 1921793

The message in the editor is a warning, the file names with spaces work
just fine in every reader that actually supports embedded fonts, I know
of. As such I dont feel the need to add processing time to the
conversion to fix a not real problem.

 status wontfix

Changed in calibre:
status: New → Won't Fix
Revision history for this message
Colin (granitestatecolin) wrote :

I understand it's not a priority, but for those who use Calibre as a conversion tool for creating ebooks, these factors do matter. Outlets like Apple (most aggressive) and Kobo and Google (less aggressive) will not accept ebook files that have warnings in the EPUB.

Revision history for this message
Kovid Goyal (kovid) wrote : Fixed in master

Fixed in branch master. The fix will be in the next release. calibre is usually released every alternate Friday.

 status fixreleased

Changed in calibre:
status: Won't Fix → Fix Released
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