<p>My client has a multi-page PDF file.  They need it split by page.  Does anyone know of a way to do this - preferably in C#.</p>

PDFSharp
is an open source library which may be what you're after:
Key Features
Creates PDF documents on the fly from any .Net language
Easy to understand object model to compose documents
One source code for drawing on a PDF page as well as in a window or on the printer
Modify, merge, and split existing PDF files
This sample
shows how to convert a PDF document with n pages into n documents with one page each.