I thought I share this with you because I spent some time before finding the solution. What I wanted to do is to simply convert a multipage TIFF image to a PDF file. I wanted this for an ASP.NET project.

TallPDF does this but you have to pay a lot for a simple task (TallPDF does other things too though!). After some searching came to the conclusion that PDF Creation Libraries are my best option here. There are a few for .NET including iTextSharp, PDFsharp and PDF Clown. I used iTextSharp because it has a sample that was showing how to create a PDF file from a multipage TIFF image (exactly what I wanted).

Here is the code that does the conversion:

            // creation of the document with a certain size and certain margins
            iTextSharp.text.Document document = new iTextSharp.text.Document(iTextSharp.text.PageSize.A4, 0, 0, 0, 0);
            
            // creation of the different writers
            iTextSharp.text.pdf.PdfWriter writer = iTextSharp.text.pdf.PdfWriter.GetInstance(document, new System.IO.FileStream(Server.MapPath("~/App_Data/result.pdf"), System.IO.FileMode.Create));

            // load the tiff image and count the total pages
            System.Drawing.Bitmap bm = new System.Drawing.Bitmap(Server.MapPath("~/App_Data/source.tif"));
            int total = bm.GetFrameCount(System.Drawing.Imaging.FrameDimension.Page);

            document.Open();
            iTextSharp.text.pdf.PdfContentByte cb = writer.DirectContent;
            for (int k = 0; k < total; ++k)
            {
                bm.SelectActiveFrame(System.Drawing.Imaging.FrameDimension.Page, k);
                iTextSharp.text.Image img = iTextSharp.text.Image.GetInstance(bm, System.Drawing.Imaging.ImageFormat.Bmp);
                // scale the image to fit in the page
                img.ScalePercent(72f / img.DpiX * 100);
                img.SetAbsolutePosition(0, 0);
                cb.AddImage(img);
                document.NewPage();
            }
            document.Close();

As you can see it is very simple and straightforward.