Guesses Type1C font type based on file content

src/core/fonts.js

@@ -19,7 +19,7 @@
            isNum, ISOAdobeCharset, Stream, stringToArray, stringToBytes,
            string32, TextDecoder, warn, Lexer, Util, FONT_IDENTITY_MATRIX,
            FontRendererFactory, shadow, isString, IdentityCMap, Name,
-           CMapFactory, PDFJS */
+           CMapFactory, PDFJS, readUint32 */
 
 'use strict';
 
@@ -2259,7 +2259,12 @@ var Font = (function FontClosure() {
     // Some fonts might use wrong font types for Type1C or CIDFontType0C
     var subtype = properties.subtype;
     if (subtype == 'Type1C' && (type != 'Type1' && type != 'MMType1')) {
-      type = 'Type1';
+      // Some TrueType fonts by mistake claim Type1C
+      if (isTrueTypeFile(file)) {
+        subtype = 'TrueType';
+      } else {
+        type = 'Type1';
+      }
     }
     if (subtype == 'CIDFontType0C' && type != 'CIDFontType0') {
       type = 'CIDFontType0';
@@ -2407,6 +2412,11 @@ var Font = (function FontClosure() {
     file.virtualOffset += data.length;
   }
 
+  function isTrueTypeFile(file) {
+    var header = file.peekBytes(4);
+    return readUint32(header, 0) === 0x00010000;
+  }
+
   /**
    * Rebuilds the char code to glyph ID map by trying to replace the char codes
    * with their unicode value. It also moves char codes that are in known

test/pdfs/.gitignore

@@ -50,6 +50,7 @@
 !bug864847.pdf
 !issue1002.pdf
 !issue925.pdf
+!issue4668.pdf
 !gradientfill.pdf
 !bug903856.pdf
 !bug850854.pdf

test/test_manifest.json

@@ -1583,6 +1583,12 @@
        "lastPage": 1,
        "type": "load"
     },
+    {  "id": "issue4668",
+      "file": "pdfs/issue4668.pdf",
+      "md5": "a749d5ca995ad745411406d29156b04e",
+      "rounds": 1,
+      "type": "eq"
+    },
     {  "id": "issue3666",
        "file": "pdfs/issue3666.pdf",
        "md5": "c2156a34b9634b174556910732ab9df0",