# UNDF: UNDF-2026-000001210
--- a/core/document_p.h
+++ b/core/document_p.h
@@ -334,6 +334,7 @@ public:
     QPointer<FontExtractionThread> m_fontThread;
     bool m_fontsCached;
     QSet<DocumentInfo::Key> m_documentInfoAskedKeys;
     DocumentInfo m_documentInfo;
     FontInfo::List m_fontsCache;
+    QSet<QString> m_fontsCacheKeys; // O(1) dedup set parallel to m_fontsCache

     QSet<View *> m_views;

--- a/core/document.cpp
+++ b/core/document.cpp
@@ -1562,9 +1562,16 @@ void DocumentPrivate::fontReadingGotFont(const Okular::FontInfo &font)
 {
-    // Try to avoid duplicate fonts
-    if (m_fontsCache.indexOf(font) == -1) {
+    // Try to avoid duplicate fonts — O(1) lookup via parallel key set
+    // Previously: m_fontsCache.indexOf(font) which is O(F) per call, O(F^2) total.
+    // Fix: build a composite key from all equality fields and use QSet for O(1) dedup.
+    const QString key = font.name()
+        + QLatin1Char('|') + font.substituteName()
+        + QLatin1Char('|') + QString::number(static_cast<int>(font.type()))
+        + QLatin1Char('|') + QString::number(static_cast<int>(font.embedType()))
+        + QLatin1Char('|') + font.file()
+        + QLatin1Char('|') + (font.canBeExtracted() ? QLatin1Char('1') : QLatin1Char('0'));
+    if (!m_fontsCacheKeys.contains(key)) {
+        m_fontsCacheKeys.insert(key);
         m_fontsCache.append(font);

         Q_EMIT m_parent->gotFont(font);
     }
 }