Four years ago, I wrote a hint about how to remove a PDF password using ColorSync from those PDF files than you can view, but not copy or change. It did not apply to files that were encrypted with a password and could not be opened.
To my surprise, it has been one of the more popular hints, with over 112,000 hits. However, since Tiger, Apple has progressively tightened the PDF DRM, so that the hint does not work in Snow Leopard any more. There are several third party programs that will do it, but here's how to do it in Snow Leopard for free.
Note that this hint will not decrypt PDF files that cannot be opened without a password.
The following do not work: copying the old ColorSync from Tiger, using a virtual CUPS-PDF printer, trying to print as PDF, and dropping the PDF onto a Pages or a Keynote document to create another PDF.
Assuming you can print the file and you have administrator rights, here is one simple way to defeat this DRM.
- In Finder, press Shift-Command-G, or select Go » Go to Folder....
- Type /var/spool and press Return.
- The spool folder will open, and inside there will be several folders. The cups folder will have a red Stop sign on it.
- Select it, and then press Command-I (or use File » Get Info).
- In the Sharing & Permissions section of the Get Info window (at the bottom), click the lock to open. You will need your administrator password.
- Now click the "+" sign and add yourself to the list. You only need 'read only' privileges.
- Now open the cups folder.
- View the cups folder as a list (View menu) and sort by Date Modified.
- Open up your favorite PostScript printer by going to Print and Fax in System Preferences and selecting it from the list on the left. If you don't have one, install one.
- Pause the printer.
- Print your PDF to this printer. It will complain that the printer is paused. Click Add to Queue and not Resume.
- The print file will show up in the cups folder at the top with an obscure name like d00023-001 (ignore the corresponding file c00023).
- Drag this print file to your Desktop (or wherever). You will need your administrator password again.
- Add .pdf to the end of the file name, and open with Preview.
- Delete the print job in your PostScript printer.
But what if Apple closes this loophole? Just set your printer to save the file after it prints, and then download it back to your computer! See this discussion for more on that subject.

