One solution on the Mac is in the Page Setup menu. ( File / Page Setup...)
Set the Paper Size to the actual size of your paper, but change the Scale to whatever percent you choose. Then, from the print dialog box select Page Scaling : None. The image size should be reduced within the overall page size.
To change the scale (by a percentage)in AA8 here is what you need to do:
1. Go to Print Setup
2. Change your printer to "Adobe PDF"
3. Select your paper size (half of your original if scaling 50%)
4. Properties>Layout>Advanced
5. There is a scaling option, change to desired scale
6. Ok>Ok>Ok
Now you are going to print your PDF to a new PDF:
1. Go to Print
2. Change your printer to "Adobe PDF"
3. Select your paper size (half of your original if scaling 50%)
4. Make sure Auto-Rotate and Center is checked
5. Uncheck "Choose Paper Source by PDF Page Size"
6. Select Page Scaling: None
7. Print > Save As a new PDF (The PDF Page Size is now scaled to what you want)
Now open the new PDF and you should be able to print it to the scale you chose without any problems.
-Ben
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