Does anyone know of an .eml to .pdf C# API?
Couldn't you just print the file to pdf?
Edit: I guess what I'm saying is rather than looking for a .eml to .pdf conversion tool; you could look for a batch printing tool that can automate the printing of 100's or 1000's of .eml's. Then you just make the tool batch print to pdf.
Use OpenOffice (http://www.openoffice.org)
This will basically convert anything to PDF (doc, xls, ppt, txt). Since eml are just txt, why not just use this? See http://www.opendocument4all.com/download/OpenOffice.net.pdf for how to use OpenOffice in C#.
We had a similar task, but on a much smaller scale and it was a temporary solution. We converted the EML files to HTML pages and then used the ABC Pdf component (I think they had a free version back then?) to create the PDF files out of the HTML pages. We did everything directly from the ASP.NET page.
Shameless plug here....
I am working on a new converter service which can convert .eml and other document types to PDF or TIFF. I am also building a web API for it. If you want, I would be happy to work with you to integrate it into your application.
Check http://www.convert.io