gistfile1.cs

private void Form1_Load(object sender, EventArgs e)
{
    var rpt = new PageReport(new FileInfo("report.rdlx"));
    var doc = new PageDocument(rpt);
    var xml = new XmlRenderingExtension();
    var settings = new Settings {Encoding = "UTF-8"};
    var streamProvider = new CustomStreamProvider(new DirectoryInfo("."), "report.xml");
    doc.Render(xml, streamProvider, settings);
}

    class CustomStreamProvider : StreamProvider
    {
        private readonly DirectoryInfo _baseDir;
        private readonly string _fileName;
        private  StreamInfo _primaryStream;
        public CustomStreamProvider(DirectoryInfo baseDir, string fileName)
        {
            _baseDir = baseDir;
            _fileName = fileName;
        }
        public override StreamInfo CreatePrimaryStream(string mimeType, string suggestedFileExtension)
        {
            _primaryStream = new CustomSreamInfo(new FileInfo(Path.Combine(_baseDir.FullName, _fileName)), mimeType);
            return _primaryStream;
        }

        public override StreamInfo CreateSecondaryStream(string relativeName, string mimeType, string suggestedFileExtension)
        {
            throw new NotImplementedException();
        }

        public override StreamInfo GetPrimaryStream()
        {
            return _primaryStream;
        }

        public override StreamInfo[] GetSecondaryStreams()
        {
            throw new NotImplementedException();
        }
    }
    class CustomSreamInfo : StreamInfo
    {
        private readonly FileInfo _file;
        public CustomSreamInfo(FileInfo fileInfo, string mimeType) : base(new Uri(fileInfo.FullName), mimeType)
        {
            _file = fileInfo;
        }

        public override Stream OpenStream()
        {
            if(_file.Exists)
                _file.Delete();
            var stream = _file.Open(FileMode.OpenOrCreate, FileAccess.ReadWrite);
            return stream;

        }
    }