Tipster Jeremy Grove discusses methods to insert PDF files into AutoCAD Civil 3D.
"Normally, when inserting a PDF file you would use the Insert OLE Object command in Civil 3D. I recently discovered that if you drag the PDF file to your workspace, it automatically inserts the PDF as an OLE object, but it does so with a transparent background instead of the usual opaque white background. This method also allows you to select the page of the PDF to be inserted, and the insertion scale. If the PDF was originally created using CAD software, the linework in the PDF will also be snappable. This little trick has saved me countless hours when trying to trace PDF files in AutoCAD to draw up quick details. It also seems to import the PDF with much nicer image quality than the Insert OLE Object command, making it easier to read."
Notes from Cadalyst Tip Patrol: PDF files are a universally accepted format of transferring data to third parties. AutoCAD and Civil 3D can't edit PDFs, but they can reference them. The PDFs can be inserted as OLE objects as described above, or they can be referenced in through the Xref Manager, just as you would a DWG file.
PDF files are inserted as an overlay, giving them certain properties such as fade control. They can be clipped (use PDFClip), scaled, rotated, and more. If the PDF was created using Autodesk's DWG to PDF tool, the linework will have layers, and can be snapped to while referenced in AutoCAD. If you are going to create PDF files of your AutoCAD/Civil 3D files, it would be useful to use the DWG to PDF printer driver in AutoCAD/Civil 3D in order to take advantage of the layering and snap features in the future.