start adding support for reading encrypted documents

src/UglyToad.PdfPig/Encryption/NoOpEncryptionHandler.cs

@@ -0,0 +1,19 @@
+namespace UglyToad.PdfPig.Encryption
+{
+    using System.Collections.Generic;
+    using Tokens;
+
+    internal class NoOpEncryptionHandler : IEncryptionHandler
+    {
+        public static NoOpEncryptionHandler Instance { get; } = new NoOpEncryptionHandler();
+
+        private NoOpEncryptionHandler()
+        {
+        }
+
+        public IReadOnlyList<byte> Decrypt(StreamToken stream)
+        {
+            return stream.Data;
+        }
+    }
+}