diff --git a/PDFiumSharp/PDFium.cs b/PDFiumSharp/PDFium.cs
index 4f8dd2e..9f3acbe 100644
--- a/PDFiumSharp/PDFium.cs
+++ b/PDFiumSharp/PDFium.cs
@@ -122,14 +122,13 @@ public static FPDF_DOCUMENT FPDF_LoadDocument(byte[] data, int index = 0, int co
         /// <summary>
         ///     Loads a PDF document from '<paramref name="count" />' bytes read from a stream.
         /// </summary>
-        /// <param name="fileRead"></param>
         /// <param name="count">
         ///     The number of bytes to read from the <paramref name="stream" />.
         ///     If the value is equal to or smaller than 0, the stream is read to the end.
         /// </param>
-        /// <param name="stream"></param>
+        /// <param name="fileRead">The FILEREAD structure ready for reading.</param>
         /// <param name="password">Pdf password</param>
-        public static FPDF_DOCUMENT FPDF_LoadDocument(Stream stream, FPDF_FILEREAD fileRead, int count = 0, string password = null)
+        public static FPDF_DOCUMENT FPDF_LoadDocument(FPDF_FILEREAD fileRead, string password = null)
             => FPDF_LoadCustomDocument(fileRead, password);
 
         //public static string FPDF_VIEWERREF_GetName(FPDF_DOCUMENT document, string key)
diff --git a/PDFiumSharp/PdfDocument.cs b/PDFiumSharp/PdfDocument.cs
index adae6ae..f2dac5f 100644
--- a/PDFiumSharp/PdfDocument.cs
+++ b/PDFiumSharp/PdfDocument.cs
@@ -19,6 +19,8 @@ public sealed class PdfDocument : NativeWrapper<FPDF_DOCUMENT>
         private FPDF_FORMFILLINFO formCallbacks;
 
         private GCHandle formCallbacksHandle;
+        
+        private FPDF_FILEREAD fileRead;
 
         private FPDF_FORMHANDLE form;
 
@@ -138,15 +140,23 @@ public PdfDocument(byte[] data, int index = 0, int count = -1, string password =
         /// Loads a <see cref="PdfDocument"/> from '<paramref name="count"/>' bytes read from a <paramref name="stream"/>.
         /// <see cref="Close"/> must be called in order to free unmanaged resources.
         /// </summary>
-        /// <param name="stream"></param>
-        /// <param name="fileRead"></param>
+        /// <param name="data">Stream containing the bytes of the PDF document to load. Must remain open and accessible as long as the document is being used.</param>
         /// <param name="count">
         /// The number of bytes to read from the <paramref name="stream"/>.
         /// If the value is equal to or smaller than 0, the stream is read to the end.
         /// </param>
-        /// <param name="password"></param>
-        public PdfDocument(Stream stream, FPDF_FILEREAD fileRead, int count = 0, string password = null)
-            : this(PDFium.FPDF_LoadDocument(stream, fileRead, count, password)) { }
+        /// <param name="password">Password.</param>
+        public PdfDocument(Stream stream, int count = 0, string password = null)
+            : this(FPDF_FILEREAD.FromStream(stream, count), password) { }
+
+        /// <summary>
+        /// Private overload which keeps the FILEREAD reference so that the delegate and its callback stub remain valid for the lifetime of the document.
+        /// </summary>
+        private PdfDocument(FPDF_FILEREAD fileRead, string password)
+		        : this(PDFium.FPDF_LoadDocument(fileRead, password)) 
+        {
+	        this.fileRead = fileRead;
+        }
 
         /// <summary>
         /// Closes the <see cref="PdfDocument"/> and frees unmanaged resources.
@@ -209,6 +219,8 @@ protected override void Dispose(FPDF_DOCUMENT handle)
 
             ((IDisposable)this.Pages).Dispose();
             PDFium.FPDF_CloseDocument(handle);
+
+            this.fileRead = null;
         }
     }
 }
\ No newline at end of file
diff --git a/PDFiumSharp/Types/FPDF_FILEACCESS.cs b/PDFiumSharp/Types/FPDF_FILEACCESS.cs
index c2c5526..044115c 100644
--- a/PDFiumSharp/Types/FPDF_FILEACCESS.cs
+++ b/PDFiumSharp/Types/FPDF_FILEACCESS.cs
@@ -12,9 +12,9 @@
 namespace PDFiumSharp.Types
 {
     [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
-    public delegate bool FileReadBlockHandler(IntPtr ignore, int position, IntPtr buffer, int size);
+    public delegate bool FileReadBlockHandler(IntPtr param, int position, IntPtr buffer, int size);
     [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
-    public delegate bool FileWriteBlockHandler(IntPtr ignore, IntPtr data, int size);
+    public delegate bool FileWriteBlockHandler(IntPtr self, IntPtr data, int size);
 
 	[StructLayout(LayoutKind.Sequential)]
     public class FPDF_FILEREAD
@@ -26,11 +26,11 @@ public class FPDF_FILEREAD
 
 		readonly IntPtr _param;
 
-		public FPDF_FILEREAD(int fileLength, FileReadBlockHandler readBlock)
+		public FPDF_FILEREAD(int fileLength, FileReadBlockHandler readBlock, IntPtr param = default)
 		{
 			_fileLength = fileLength;
 			_readBlock = readBlock;
-			_param = IntPtr.Zero;
+			_param = param;
 		}
 
 		public static FPDF_FILEREAD FromStream(Stream stream, int count = 0)
@@ -38,17 +38,40 @@ public static FPDF_FILEREAD FromStream(Stream stream, int count = 0)
 			if (count <= 0)
 				count = (int)(stream.Length - stream.Position);
 			var start = stream.Position;
+
+			var memoryStream = stream as MemoryStream;
+			if (memoryStream != null) {
+				try {
+					memoryStream.GetBuffer();
+				} catch (UnauthorizedAccessException) {
+					// Buffer is not public, and thus not directly usable
+					memoryStream = null;
+				}
+			}
+
 			byte[] data = null;
-			FPDF_FILEREAD fileRead = new FPDF_FILEREAD(count, (ignore, position, buffer, size) =>
-			{
-				stream.Position = start + position;
-				if (data == null || data.Length < size)
-					data = new byte[size];
-				if (stream.Read(data, 0, size) != size)
-					return false;
-				Marshal.Copy(data, 0, buffer, size);
-				return true;
-			});
+			FPDF_FILEREAD fileRead = memoryStream != null 
+					? new FPDF_FILEREAD(count, (_, position, buffer, size) => 
+						{
+							if (position < 0 || size <= 0 || start+position+size > memoryStream.Length) 
+								return false;
+							var streamBuffer = memoryStream.GetBuffer();
+							Marshal.Copy(streamBuffer, (int)start+position, buffer, size);
+							return true;
+						})
+					: new FPDF_FILEREAD(count, (_, position, buffer, size) =>
+						{
+							if (position < 0 || size <= 0)
+								return false;
+							stream.Seek(start + position, SeekOrigin.Begin);
+							if (data == null || data.Length < size)
+								data = new byte[size];
+							if (stream.Read(data, 0, size) != size)
+								return false;
+							
+							Marshal.Copy(data, 0, buffer, size);
+							return true;
+						});
 			return fileRead;
 		}
     }