You can bring in images and pdfs from the catalog in ArcMap. However, if they have no spatial reference, you must georeference the images, so they match the projection and scale.
Some good links to help you georeferencing.
http://resources.arcgis.com/en/help/main/10.2/index.html#//009t000000mn000000
http://resources.arcgis.com/en/help/main/10.2/index.html#/Georeferencing_toolbar_tools/009t000000mp0...
I made a mistake there, you cannot bring PDFs in. However, it usually is a simple matter to convert the pdf to a jpg(or other raster type) and bring it in.
Thanks, Ian. I was able to do this on Adobe Photoshop.
David