Briksoftware has announced PDFKey Pro 4.0 (http://pdfkey.com) for OS X and Windows.

PDFKey Pro is a utility that locks and unlocks password-protected PDF documents. You can lock PDF files by creating perfect copies. Users may protect with either (or both), a viewing password and a password to restrict usage permissions and more.

PDFKey Pro requires Mac OS X 10.7 or higher It costs $24.99. A demo is available for download.