The same PDF displays fine on one computer, then some text turns into boxes or gets swapped for a completely different font on another — the cause is almost always how the font was, or wasn't, embedded.
Two ways to handle fonts
When a PDF is generated, the producing software faces a choice:
- Embedded: the font file itself (or at least the glyph data actually used) is packed directly into the PDF. File size grows somewhat, but the display is identical no matter which computer opens it.
- Not embedded, relying on the system font: the PDF only records "this text uses font X" — how it actually renders depends on whether the opening computer has that font installed. If not, the reader substitutes an approximate font, and the visual difference can be significant.
Why boxes or garbled text show up
Boxes (sometimes called "tofu") typically appear for special symbols or uncommon characters — when the reader genuinely can't find any font capable of displaying that character, it shows a placeholder box instead. CJK text (Chinese, Japanese, Korean), with its much larger character sets, is far more prone to this than Latin text when the right font isn't properly embedded.
Why professional software usually recommends embedding fonts
For any file shared across devices and operating systems — which is essentially every formal document use case — embedding fonts is the only reliable way to guarantee consistent display. Many professional layout and office tools default to embedding fonts when exporting a PDF, especially for documents involving non-Latin text (Chinese, Arabic, etc.).
Subsetting: embedded without bloating the file
Embedding an entire font file directly (a CJK font can be tens of MB) would balloon file size. The more common approach is "subsetting" — embedding only the glyph data for characters actually used in the document. A document using a few hundred Chinese characters might only add tens to a few hundred KB through subsetting, instead of the tens of MB a whole font file would cost.
How fonts get handled when you edit a PDF
When you add or edit text with LocalPDF, any CJK characters you use get automatically subsetted and embedded into the exported file — no boxes or garbled text. Existing text that already had its original font embedded stays exactly as it was. For the font-substitution logic used when editing existing text, see our article on avoiding font mismatches.
Now that you know how font embedding works, add CJK content with more confidence.
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