use encoding specified in base font if present

if the font uses a named encoding which is not recognised, use the corresponding encoding based on the base font name, or fall back to windows ansi encoding.

src/UglyToad.PdfPig.Fonts/Encodings/SymbolEncoding.cs

@@ -1,6 +1,9 @@
 namespace UglyToad.PdfPig.Fonts.Encodings
 {
-    internal class SymbolEncoding : Encoding
+    /// <summary>
+    /// Symbol encoding.
+    /// </summary>
+    public class SymbolEncoding : Encoding
     {
         private static readonly (int, string)[] EncodingTable = {
             (0101, "Alpha"),
@@ -194,8 +197,12 @@
             (0172, "zeta")
         };
 
+        /// <summary>
+        /// Single instance of this encoding.
+        /// </summary>
         public static SymbolEncoding Instance { get; } = new SymbolEncoding();
 
+        /// <inheritdoc />
         public override string EncodingName => "SymbolEncoding";
 
         private SymbolEncoding()

src/UglyToad.PdfPig.Fonts/Encodings/WinAnsiEncoding.cs

@@ -2,7 +2,10 @@
 {
     using Core;
 
-    internal class WinAnsiEncoding : Encoding
+    /// <summary>
+    /// Windows ANSI encoding.
+    /// </summary>
+    public class WinAnsiEncoding : Encoding
     {
         /// <summary>
         /// The encoding table is taken from the Appendix of the specification.
@@ -231,8 +234,12 @@
             (0255, "hyphen")
         };
 
+        /// <summary>
+        /// Single instance of this encoding.
+        /// </summary>
         public static WinAnsiEncoding Instance { get; } = new WinAnsiEncoding();
 
+        /// <inheritdoc />
         public override string EncodingName => "WinAnsiEncoding";
 
         private WinAnsiEncoding()

src/UglyToad.PdfPig.Fonts/Encodings/ZapfDingbatsEncoding.cs

@@ -1,6 +1,9 @@
 namespace UglyToad.PdfPig.Fonts.Encodings
 {
-    internal class ZapfDingbatsEncoding : Encoding
+    /// <summary>
+    /// Zapf Dingbats encoding.
+    /// </summary>
+    public class ZapfDingbatsEncoding : Encoding
     {
         private static readonly (int, string)[] EncodingTable = {
             (040, "space"),
@@ -193,8 +196,12 @@
             (0376, "a191")
         };
 
+        /// <summary>
+        /// Single instance of this encoding.
+        /// </summary>
         public static ZapfDingbatsEncoding Instance { get; } = new ZapfDingbatsEncoding();
 
+        /// <inheritdoc />
         public override string EncodingName => "ZapfDingbatsEncoding";
 
         private ZapfDingbatsEncoding()

src/UglyToad.PdfPig/PdfFonts/Parser/EncodingReader.cs

@@ -1,5 +1,6 @@
 namespace UglyToad.PdfPig.PdfFonts.Parser
 {
+    using System;
     using System.Collections.Generic;
     using Fonts;
     using Fonts.Encodings;
@@ -27,7 +28,25 @@
 
             if (baseEncodingObject is NameToken name)
             {
-                return GetNamedEncoding(descriptor, name);
+                if (TryGetNamedEncoding(descriptor, name, out var namedEncoding))
+                {
+                    return namedEncoding;
+                }
+
+                if (fontDictionary.TryGet(NameToken.BaseFont, pdfScanner, out NameToken baseFontName))
+                {
+                    if (string.Equals(baseFontName.Data, "ZapfDingbats", StringComparison.OrdinalIgnoreCase))
+                    {
+                        return ZapfDingbatsEncoding.Instance;
+                    }
+
+                    if (string.Equals(baseFontName.Data, "Symbol", StringComparison.OrdinalIgnoreCase))
+                    {
+                        return SymbolEncoding.Instance;
+                    }
+
+                    return WinAnsiEncoding.Instance;
+                }
             }
 
             DictionaryToken encodingDictionary = DirectObjectFinder.Get<DictionaryToken>(baseEncodingObject, pdfScanner);
@@ -100,9 +119,9 @@
             return differences;
         }
 
-        private static Encoding GetNamedEncoding(FontDescriptor descriptor, NameToken encodingName)
+        private static bool TryGetNamedEncoding(FontDescriptor descriptor, NameToken encodingName, out Encoding encoding)
         {
-            Encoding encoding;
+            encoding = null;
             // Symbolic fonts default to standard encoding.
             if (descriptor?.Flags.HasFlag(FontDescriptorFlags.Symbolic) == true)
             {
@@ -111,11 +130,10 @@
 
             if (!Encoding.TryGetNamedEncoding(encodingName, out encoding))
             {
-                // TODO: PDFBox would not throw here.
-                throw new InvalidFontFormatException($"Unrecognised encoding name: {encodingName}");
+                return false;
             }
 
-            return encoding;
+            return true;
         }
     }
 }