If you see (Not Responding) in the title bar of the Design program when inserting a PDF, this is likely because the PDF is too large (D Size or larger). You will need to ask your source to provide you with a C size (18×24) or smalller PDF.
Alternatively you can make the PDF smaller, but in order for you to do this, you would need to use a PDF creator or you can download CutePDF and follow the instructions in this PDF: CutePDF Instructions Resize PDF
Once you have the smaller PDF, open DS|Design and follow the instruction from the manual section entitled “Inserting a PDF or Raster Image from a File” & “Resizing an Image to the Drawing Scale” on pages 13.13 and 13.18 in the DS|Design user manual.