No Board outline when artwork is made

 Hello,

I have a PDF called A basic intrduction to Cadence Orcad (Allegro) 16.2 PCB Designer.

I have been following that to help me learn  this program, so far it has worked but when I make the artwork (gerber files) Fig.25 says the Board Outline is not included in the films. Why is that? the PDF doesn't give me a reason why. 

 Doesn't the PCB Manufacture need the outline to make the board?

The PCB software I use now is Orcad Layout 9.0 and I can make outlines for the Artwork (gerber files).

Any help is appreaciated...

Thanks, Dennis