Here is another way. Download DWF Writer from Autodesk (it’s free), then open your PDF in Acrobat (reader is fine) and plot the PDF to a DWF using the DWF Writer print driver. Note that multi sheet PDFs are converted to a multi sheet DWF.
Then use the reference manager or the ._DWFATTACH command in AutoCAD to reference the DWF file. (The ability to reference DWF files was added in AutoCAD 2007).
Now if there was just some way to create a reference to each sheet in the DWF all at once rather than having to repeat the ._DWFATTACH command for each one.