Remove the tag for missing font subset when trying to find a substitution

Fixes #17929.

src/core/evaluator.js

@@ -4261,7 +4261,8 @@ class PartialEvaluator {
             this.idFactory,
             this.options.standardFontDataUrl,
             baseFontName,
-            standardFontName
+            standardFontName,
+            type
           );
         }
 
@@ -4381,7 +4382,8 @@ class PartialEvaluator {
           this.idFactory,
           this.options.standardFontDataUrl,
           fontName.name,
-          standardFontName
+          standardFontName,
+          type
         );
       }
     }

src/core/font_substitutions.js

@@ -456,6 +456,7 @@ function generateFont(
  * @param {String} baseFontName The font name to be substituted.
  * @param {String|undefined} standardFontName The standard font name to use
  *   if the base font is not available.
+ * @param {String} type The font type.
  * @returns an Object with the CSS, the loaded name, the src and the style.
  */
 function getFontSubstitution(
@@ -463,12 +464,21 @@ function getFontSubstitution(
   idFactory,
   localFontPath,
   baseFontName,
-  standardFontName
+  standardFontName,
+  type
 ) {
   if (baseFontName.startsWith("InvalidPDFjsFont_")) {
     return null;
   }
 
+  if (
+    (type === "TrueType" || type === "Type1") &&
+    /^[A-Z]{6}\+/.test(baseFontName)
+  ) {
+    // When the font is a subset, we need to remove the prefix (see 9.6.4).
+    baseFontName = baseFontName.slice(7);
+  }
+
   // It's possible to have a font name with spaces, commas or dashes, hence we
   // just replace them by a dash.
   baseFontName = normalizeFontName(baseFontName);