you haven't described this very clearly... what I'm picturing in my head from your description is a shape with nothing around it. How do you make nothing transparent? Use the save to web tool and save it as a gif. Otherwise you will always see the artboard as white behind the shape.

'Nothing around it' is 'white paper' space if you will. It is white, but still opaque. I want to make this white paper space transparent, whilst leaving the shape in the centre opaque.
Hopefully this is clearer!

This is CS1 I'm using btw - yeah, i know..

Transparent over what? Print on transparent paper, or use the save to web utility described above to generate an image with a transparent background. Basically, in order for your eye to recognize transparency, there's got to be something behind the transparent area to be percieved... i.e. you wouldn't know that a piece of glass was transparent if you couldn't see anything on the other side of the glass. So what are you trying to see through to?

Okay.
Let's just say my A3 AI file is completely covered with a red square.
When I place my PDF in this AI file over that red square, I want see that red square right up to the very perimeter of my shape.
At the moment, when I place the PDF, I see my shape in the centre of it's white PDF page, then the red surrounding this box.

If my shape was simply rectangular for example, I would draw a rectangle of the shape and make a clipping mask. I know this isn't making the 'white space' transparent but the effect is the same. My shape is not rectangular, but organic, so this is not an option..

Cheers.

rectangle *over* the shape

ps. The PDF I'm importing is a screen capture from SU. From Layout. So I guess it is not actually a vector shape. More like a JPEG..

ah. Well, then you can either a) create a clipping mask using the pen tool, which will let you do what you would do with a rectangle, only control the clipping mask boundary to be the same as the boundary of your shape. OR, b) use the live trace tool to turn that raster into a vector, and tell the live trace tool to 'ignore white'.

I don't think i have the live trace tool in CS1.

The pen tool sounds about right, but the outline of the shape is very complex so that may be hard.

Surely there is another way? I mean, I know there is another way.. Anyone?

oh this might be help
you said the file was bitmap based, not vector right?
then take it to photoshop, delete white space and keep background as transparent. Then, save it as .png format and load it to illustrator.
All the white areas you deleted will appear transparent
send me an e-mail if you need more help

^ yep, thanks. i know this option exists, but i don't want to have to deal with huge ps files within my already large ai file..

i'm sure this can be done another way within ai..

just go into ps, it's made to deal with pixels and ai is for vectors...and if you want smaller files try placing your files as links in ai and not embed them. you could also render your image instead of screenprint, and save it as png or gif or anything that can save with transparancy.

i thought if you magic wanded the area in question you'd be able to control that selection and thereby its transparency settings?

magic wand won't work for some reason
in fact, im not at all familiar with the wand in AI, but if it's anything like PS, i still can't get it to work..

you might need to duplicate the layer to get the wand to work.

does changing it's blending mode to "multiply" help? That usually drops the white pixels from a layer

doesn't SU do vector output? What happens if you print the Layout view to a PDF printer? Does the PDF end up raster or vector?

depending on your image, you might be able to just set the blending mode of the image to 'difference' in the transparency palette.

if your image is a raster image with no transparency, you can't acheive what you want in illustrator alone. Multiply will get you halfway there with making white transparent but the rest will exhibit transparency effects.

You'll have to clip out in photoshop the areas you want transparent and save as a PNG or TIFF with transparency. i usually just clip and delete the transparent areas. then make sure there's no "background" layer in PS meaning you should see the default checkerboard pattern in transparent areas. make sure it's all one layer and save as a PNG file.

Then bringing this back into illustrator will have those areas clipped.