Handle non seekable stream by copying it into a memory stream and fix #1146

src/UglyToad.PdfPig/Parser/PdfDocumentFactory.cs

@@ -44,9 +44,23 @@
 
         internal static PdfDocument Open(Stream stream, ParsingOptions? options)
         {
-            var streamInput = new StreamInputBytes(stream, false);
+            StreamInputBytes streamInput;
+            long initialPosition;
             
-            var initialPosition = stream.Position;
+            if (stream is { CanRead: true, CanSeek: false })
+            {
+                // We need the stream to be seekable
+                var ms = new MemoryStream();
+                stream.CopyTo(ms); // Copy the non seekable stream in memory (seekable)
+                ms.Position = 0;
+                streamInput = new StreamInputBytes(ms, true); // The created memory stream will be disposed on document dispose
+                initialPosition = ms.Position;
+            }
+            else
+            {
+                streamInput = new StreamInputBytes(stream, false);
+                initialPosition = stream.Position;
+            }
 
             try
             {

src/UglyToad.PdfPig/PdfDocument.cs

@@ -112,10 +112,14 @@
 
         /// <summary>
         /// Creates a <see cref="PdfDocument"/> for reading from the provided stream.
+        /// <para>
+        /// If the stream provided is not seekable (<see cref="Stream.CanSeek"/> is <c>false</c>), the stream will be copied into a new <see cref="MemoryStream"/>.
+        /// </para>
         /// The caller must manage disposing the stream. The created PdfDocument will not dispose the stream.
         /// </summary>
         /// <param name="stream">
         /// A stream of the file contents, this must support reading and seeking.
+        /// <para>If the stream provided is not seekable (<see cref="Stream.CanSeek"/> is <c>false</c>), the stream will be copied into a new <see cref="MemoryStream"/>.</para>
         /// The PdfDocument will not dispose of the provided stream.
         /// </param>
         /// <param name="options">Optional parameters controlling parsing.</param>