The appropriate 32 or 64 bit Cairo DLLs are included in the wx package - see site-packages\wx\libcairo-2.dll for example as one of the half dozen required dll files. You still need to install the Python bindings that access these by running pip install cairocffi which will install cairocffi plus the dependent packages cffi and pycparser.
Probably the best way to check you have Cairo working is via the Demo and running Cairo, Cairo_Snippets and PDFViewer from the Miscellaneous section.
I am surprised you are getting the ImportError when you load wx.lib.pdfviewer, unless you are stepping through with a debugger or something, as the Cairo import is wrapped by a try: which then uses wx.GraphicsContext if Cairo isn’t available.
Regards,
David Hughes