Black is Not Black

I can make a box in Freehand and fill it with black and it looks perfectly black on the screen. When I print to a pdf file, my black turns out to be a lighter shade of black. I have tested making a black box in freehand with a black fill and importing a black box made from photoshop to a .tif file. When I make the pdf, the black filled box is a lighter shade of black while the imported .tif file remains black. Use this link to see the example i'm talking about: http://usproducts.com/111.pdf

Why is this happening and how can I fix it?

thanks,

Nick