Import is the command you want.
In the Import File dialog, you need to pick All Files or filter on PDF or IGES.
command does support PDF. However, it imports only the vector geometry, not the raster.
So you may not get exactly what you were expecting.
The PictureFrame command is a good option for images, however does not support the PDF format directly. If you have a PDF you will need to convert it to a JPG, PNG or other support raster format. Adobe Acobat, full purchase version, offers this. Otherwise you can screen capture for image file using built or free Mac features.
There is a custom scaling for the PDF Import.
If you have moved past that, that you need to scale the geometry with the [Scale] command. There you can pick a distance and then enter the number you want the distance to be. Rhino will calculate the scale factor for you. It is up to you!
Let us know if you have any additional questions.