I have just had a customer asking this question and the solution is not as straight forward as one might think.
The steps are:
1. Open the PDF file in Adobe Acrobat Reader and get to the desired page.
2. Minimize the Adobe Acrobat Reader. Do not close it at this point.
3. Drag and drop the PDF file from Windows Explorer on to the drawing.
4. Close Adobe Acrobat Reader.
5. Go to Step 1 for adding other pages of the same document.
Alin Vargatu, CSWP, CSWP-Sheet Metal
Javelin Technologies
Oakville Ontario Canada