public void Tiff2Pdf()
{
    using (var api = OcrApi.Create())
    {
        api.Init(Languages.English);
        //Create the renderer to PDF file output. The extension will be added automatically
        using (var renderer = OcrPdfRenderer.Create("multipage_pdf_file", "c:\\YourApp\\tessdata\\"))
        {
            renderer.BeginDocument("Title");
            api.ProcessPages(@"c:\multipage.tif", null, 0, renderer);
            renderer.EndDocument();
        }
    }
}

static void Main(string[] args)
{
	PdfCommon.Initialize();

	double scaleFactor = 1;
	var ocr = OcrApi.Create();
	ocr.Init(Languages.English);

	using (var renderer = OcrPdfRenderer.Create(@"d:\3\multipage_pdf_file", "tessdata\\"))
	{
		renderer.BeginDocument("document title");

		int i = 0;
		using (var doc = PdfDocument.Load(@"d:\3\review.pdf"))
		{
			foreach (var page in doc.Pages)
			{
				Console.WriteLine(string.Format("Page {0}", i++));
				int width = (int)(page.Width * scaleFactor);
				int height = (int)(page.Height * scaleFactor);
				using (var bitmap = new PdfBitmap(width, height, true))
				{
					bitmap.FillRect(0, 0, width, height, Color.White);
					page.Render(bitmap, 0, 0, width, height, PageRotate.Normal, RenderFlags.FPDF_LCD_TEXT);
					ocr.ProcessPage(OcrPix.FromBitmap(bitmap.Image as Bitmap), null, 0, renderer);
				}
			}
		}
		renderer.EndDocument();
	}
	ocr.Dispose();
}