NOTE: Please read the comments, as well as my “Later Notes” at the end of this post. While this post and the solutions offered by commenters all provide improved methods for cropping PDFs, there are still some catches.
If you’ve ever used the Crop tool in Acrobat, you’ve probably discovered that it doesn’t really crop: it just masks out content. Other applications may ignore the mask and reveal the stuff you were trying to delete. And since content is not deleted, there’s no reduction in file size.
Here, I’ve added a big honking half-inch bleed in Illustrator to make it obvious. The red border is the bleed (natch).
Let’s say I want to delete the bleed, just leaving the trim area of the PDF. I could use the Crop tool, but that’s not exact. Instead, knowing that I have 0.5″ bleed, I launch the Set Page Boxes tool under the Print Production tools. I choose CropBox from the pulldown at the top of the dialog, and enter 0.5″ in all the Margin Control fields. When I click OK, it appears that I have cropped the PDF to the trim. Whee!
But heartbreak awaits me when I return to the Set Page Boxes dialog to check it…Doh! The rind isn’t gone! Like a persistent zombie in a bad horror flick, it’s still there.