arcmap does not natively support pdf file format.
you can ...

1. convert your pdf to an image file format. (like jpg, png, tif, etc)
   I use irfanview with the pdf plugin to do this.
2. purchase a third party product like terrago publisher.

arcmap does not natively support pdf file format.
you can ...

1. convert your pdf to an image file format. (like jpg, png, tif, etc)
   I use irfanview with the pdf plugin to do this.
2. purchase a third party product like terrago publisher.
   EDIT:
   I just noticed that you are probably wanting to insert as an image.
   #1 or some derivative will do that.
   In fact file saveas in adobe will do that. (I have pro so not sure if it is in the free reader).