The software world is full of PDF utilities from the four corners of the globe. PSW-soft's Guaranteed PDF Decrypter (GuaPDF) is an example; its developers' page is called Russian Password Crackers, which sounds like something out of the Cold War but in fact is a group specializing in cryptosecurity. GuaPDF is designed to remove various restrictions from PDF files, up to 256-bit key encryption, and to decrypt 40-bit key passwords of any length in any language. It can also harness the processing power of Nvidia CUDA-capable graphics cards to accelerate decryption.
GuaPDF downloads as a ZIP file but opens immediately and runs locally on your PC; there's no need to install anything. This compact program doesn't modify the files it handles in any way, which is part of the decryption guarantee. Right-clicking its System Tray icon accesses the program and an option to choose the decryption's priority in accessing system resources. The interface itself is about as basic as it gets, just a PDF-based interactive dialog with File, Options, and Help menus, progress bars for the key space and the current key, and a main display. We tried several PDFs; GuaPDF quickly identified all characteristics, but the free demo version wouldn't fully decrypt the larger files. Smaller files decrypted instantly, though.
You don't need to be an industrial spy to require PDF decryption; all you need to be is forgetful. We tested GuaPDF in both Windows 7 and Vista with excellent results. It's available in several licensing configurations for regular and commercial users.