我能够通过将流文档内容保存为.DOCX并使用 Microsoft.Office.Interop.Word

I was able to solve my problem by saving the flowdocument content to .DOCX and converting it to PDF by using Microsoft.Office.Interop.Word

using moiw = Microsoft.Office.Interop.Word;


public static void WordToPDF(string docFileName)
    {
        // Create a new Microsoft Word application object
        moiw.Application word = new moiw.Application();

        // C# doesn't have optional arguments so we'll need a dummy value
        object oMissing = Missing.Value;

        // Get a Word file
        FileInfo wordFile = new FileInfo(docFileName);

        word.Visible = false;
        word.ScreenUpdating = false;

        // Cast as Object for word Open method
        Object filename = (Object)wordFile.FullName;

        // Use the dummy value as a placeholder for optional arguments
        moiw.Document doc = word.Documents.Open(ref filename, ref oMissing,
            ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing,
            ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing,
            ref oMissing, ref oMissing, ref oMissing, ref oMissing);
        doc.Activate();

        object outputFileName = wordFile.FullName.Replace(".docx", ".pdf");
        object fileFormat = moiw.WdSaveFormat.wdFormatPDF;

        // Save document into PDF Format
        doc.SaveAs(ref outputFileName,
            ref fileFormat, ref oMissing, ref oMissing,
            ref oMissing, ref oMissing, ref oMissing, ref oMissing,
            ref oMissing, ref oMissing, ref oMissing, ref oMissing,
            ref oMissing, ref oMissing, ref oMissing, ref oMissing);

        // Close the Word document, but leave the Word application open.
        // doc has to be cast to type _Document so that it will find the
        // correct Close method.                
        object saveChanges = moiw.WdSaveOptions.wdDoNotSaveChanges;
        ((moiw._Document)doc).Close(ref saveChanges, ref oMissing, ref oMissing);
        doc = null;

        // word has to be cast to type _Application so that it will find
        // the correct Quit method.
        ((moiw._Application)word).Quit(ref oMissing, ref oMissing, ref oMissing);
        word = null;
    }