Flash of Unstyled Text if Source Pdf has embedded subset font

GroupDocs.Viewer Product Family
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1

Hi GroupDocs Support,

I encountered an issue when previewing a PDF file using GroupDocs.Viewer.

The problem appears to occur because the PDF contains an embedded subset font in Base64 format. The browser needs to decode the Base64 before the font can be used, which results in a brief flash of unstyled text.

Steps to Reproduce:

  1. Open this file (
    GroupDocs Example.pdf (149.5 KB)) using GroupDocs.Viewer
  2. You can reproduce this issue easier by reducing your browser’s CPU performance (You can reduce it in Developer Tools > Performance Tab)
  3. You should be able to see the unstyled text appear briefly.

Reference:
Before Font:
Before.png (6.9 KB)

After Font:
After.png (8.7 KB)

2

The brief flash of unstyled text happens because the PDF uses a Base64 embedded subset font that the browser needs to decode before rendering. This is expected behavior.

To reduce it, you can try fully embedding fonts, flattening text layers in the PDF, or optimizing browser performance.