Hi,
Very sorry for the long delay in response. I have been heads-down in a rather difficult but very cool Open XML project – I’ll be blogging on this within the next two days.
The Open-Xml-SDK is capable of creating any Open XML document. It is only a matter of creating the right markup, the right parts with the right XML or binary content, and creating proper content and relationship types. Key point is to use the Open XML SDK Productivity Tool to help you figure out what that is.
I don’t have any specific experience on embedding PDFs into presentations. I have successfully created files with embedded OLE objects, so I do know it is possible. Make sure that your content types and relationship types are correct.
Sorry again for the slow response.