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)
When I needed to do this I saved the FlowDocument as an XPS file and finally converted to PDF with PDFSharp and deleted the XPS file

```
var test = (IDocumentPaginatorSource)flowDoc;
XpsDocument xpsDocument = new XpsDocument(xpsFileLocation, FileAccess.ReadWrite);
XpsDocumentWriter writer = XpsDocument.CreateXpsDocumentWriter(xpsDocument);
writer.Write(test.DocumentPaginator);
xpsDocument.Close();            

PdfSharp.Xps.XpsConverter.Convert(xpsFileLocation, pdfFileLocation, 0);
File.Delete(xpsFileLocation);

```

Hope this helps someone