I am running into the same issue again.  If this thread is closed, I will open a new one.

I am writing a quick method to merge several PDFs:

 public string Merge(string OutputPath, List<string> MergeFilePaths, out string Errors)
        {
            Errors = null;
            DocumentConverter Converter = new DocumentConverter();
            if (!string.IsNullOrEmpty(Errors))
                return null;
            string TempDir = Utils.GetTempDir();
            PdfFormatProvider PdfFormatProvider = new PdfFormatProvider();
            RadFlowDocument MergeIntoDocument = new RadFlowDocument();
            foreach (string OnePath in MergeFilePaths)
            {
                string ConvertedPath = Converter.ConvertFileIfNecessary(OnePath, "pdf", out Errors);
                ConvertedPath = ConvertedPath.Replace("\\", "/").Replace(TempDir, "/MedusaTemp");  // Make virtual
                if (!string.IsNullOrEmpty(Errors))
                    return null;
                using (Stream OnceStream = File.OpenRead(ConvertedPath))
                {
                    RadFlowDocument OneDocument = PdfFormatProvider.Import(OnceStream);
                    MergeIntoDocument.Merge(OneDocument);
                }
            }
            File.WriteAllBytes(OutputPath, PdfFormatProvider.Export(MergeIntoDocument));
            return OutputPath;
        }

Given my past experience, I am converting paths to virual, even though not sure why it matters as PdfFormatProvider is importing from a stream.  I still get "'Import not supported." when PdfFormatProvider.Import(OnceStream)

Example of the path value in absolute and virtual is:

ConvertedPath "/MedusaTemp/Test.pdf" string
System.Web.Hosting.HostingEnvironment.MapPath(ConvertedPath) "C:\\MedusaTemp\\Test.pdf" string

The stream that is opened looks good and has correct length.  

What am I missing?