[syncfusion_flutter_pdfviewer] Font rendering issue

[minhto2811]

Bug description

When rendering a PDF with Vietnamese text in the syncfusion_flutter_pdfviewer widget, the font appears corrupted or not properly rendered, as shown in the attached image. The text should appear correctly, but it does not.

Steps to reproduce

1. Use syncfusion_flutter_pdfviewer to load a PDF file containing Vietnamese text.
2. The text appears corrupted, with missing or incorrect characters

De_kiem_tra_hoc_ki_II_so_4_-Lich_su-_Lop_9.pdf

Code sample

Code sample

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Screenshots or Video

Screenshots / Video demonstration

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Stack Traces

Stack Traces

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On which target platforms have you observed this bug?

Android, iOS

Flutter Doctor output

Doctor output

[√] Flutter (Channel stable, 3.35.4, on Microsoft Windows [Version 10.0.26100.6899], locale en-US) [222ms]
    • Flutter version 3.35.4 on channel stable at C:\flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision d693b4b9db (8 weeks ago), 2025-09-16 14:27:41 +0000
    • Engine revision c298091351
    • Dart version 3.9.2
    • DevTools version 2.48.0
    • Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop, enable-android, enable-ios,
      cli-animations, enable-lldb-debugging

[immankumarsync]

Hi @minhto2811,

We were able to replicate the reported issue where some characters are not rendered on the PDF page on the provided PDF document. Currently, we are validating this issue, and we will provide further updates on November 13, 2025.

Regards,
Imman Kumar P

[immankumarsync]

Hi @minhto2811,

We have analyzed the provided PDF document and found that the glyphs not rendered in the document are using a font that is either not embedded in the PDF or not available in the system fonts.

Please refer to the image below for the fonts used in the provided PDF document, as shown in the Document Properties option in Adobe Reader.

• Arial,BoldItalic (system font)
• Symbol (partially embedded)
• Times-BoldItalic, Times-Italic, Times-Roman (system fonts)
• TimesNewRoman, TimesNewRoman,Bold, TimesNewRoman,Italic (not embedded)

The provided document relies on system fonts for rendering accented glyphs if the fonts are not embedded in the PDF document. If the required font is not available in the system fonts or embedded fonts, the renderer will attempt to substitute a similar font. However, accented characters may not be included in the substituted font, resulting in them not being rendered.

To ensure all glyphs render correctly across platforms, you should embed the fonts during PDF creation or export. This prevents the viewer from relying on system fonts.

Regards,
Imman Kumar P