throw informative exception when the document is encrypted

src/UglyToad.Pdf/Parser/PdfDocumentFactory.cs

@@ -123,6 +123,11 @@
         private static CosBase ParseTrailer(IRandomAccessRead reader, CrossReferenceTable crossReferenceTable,
             DynamicParser dynamicParser, BruteForceSearcher bruteForceSearcher, CosObjectPool pool, bool isLenientParsing)
         {
+            if (crossReferenceTable.Dictionary.ContainsKey(CosName.ENCRYPT))
+            {
+                throw new NotSupportedException("Cannot currently parse a document using encryption: " + crossReferenceTable.Dictionary);
+            }
+
             foreach (var value in crossReferenceTable.Dictionary.Values)
             {
                 if (value is CosObject temporaryObject)

src/UglyToad.Pdf/PdfDocument.cs

@@ -64,8 +64,20 @@
             Pages = new Pages(log, Catalog, pdfObjectParser, pageFactory, reader, isLenientParsing);
         }
 
+        /// <summary>
+        /// Creates a <see cref="PdfDocument"/> for reading from the provided file bytes.
+        /// </summary>
+        /// <param name="fileBytes">The bytes of the PDF file.</param>
+        /// <param name="options">Optional parameters controlling parsing.</param>
+        /// <returns>A <see cref="PdfDocument"/> providing access to the file contents.</returns>
         public static PdfDocument Open(byte[] fileBytes, ParsingOptions options = null) => PdfDocumentFactory.Open(fileBytes, options);
-        public static PdfDocument Open(string filename, ParsingOptions options = null) => PdfDocumentFactory.Open(filename, options);
+        /// <summary>
+        /// Opens a file and creates a <see cref="PdfDocument"/> for reading from the provided file path.
+        /// </summary>
+        /// <param name="filePath">The full path to the file location of the PDF file.</param>
+        /// <param name="options">Optional parameters controlling parsing.</param>
+        /// <returns>A <see cref="PdfDocument"/> providing access to the file contents.</returns>
+        public static PdfDocument Open(string filePath, ParsingOptions options = null) => PdfDocumentFactory.Open(filePath, options);
 
         /// <summary>
         /// Get the page with the specified page number.