Question: How would ya'll recommend that I convert a FlowDocument to PDF to be attached to an EMail?

The FlowDocument is dynamic, not static.

I would prefer to be able to store the PDF in memory as a byte[], rather than on disk, but that is negotiable.

Thanks for your help!

Answer: 
You have two options that I know of.

The first is to use a proprietary library called [NiPDF](http://nixps.com/nipdf/index.html), alternatively you can use Word Interop.

1. Save the FlowDocument to a DOCX file using [Open XML SDK](http://msdn.microsoft.com/en-us/library/bb448854.aspx)
2. Use Word Interop to load the saved document from some temporary store
3. Set the [WdSaveFormat](http://msdn.microsoft.com/en-us/library/bb238158%28v=office.12%29.aspx) to wdFormatPDF
4. Save the document again (remember to rename the file to PDF)

You can find further info [here](http://msdn.microsoft.com/de-de/library/microsoft.office.interop.word%28v=office.12%29.aspx)
I managed to get this working with the PDFCreator printer driver. You need to install the driver for this to work, so it may not be an ideal solution for some people. There is a COM interface available. The code more or less looks something like this:

```
        PDFCreator.clsPDFCreator _PDFCreator;
        PDFCreator.clsPDFCreatorError pErr;

        if (_PDFCreator.cStart(parameters, false))
        {
            _PDFCreator.cClearCache();
            _PDFCreator.set_cOption("UseAutosave", 1);
            _PDFCreator.cPrinterStop = false;
        }

        _PDFCreator.set_cOption("AutosaveFilename", file);
        _PDFCreator.set_cOption("AutosaveDirectory", folder);

    PrintDialog printDialog = new PrintDialog();                          
    printDialog.PrintDocument(((IDocumentPaginatorSource)flowDoc).DocumentPaginator, "Report");

```