Balsamiq announced that Mockups now supports export of multiple canvases to a single PDF that includes links. This means that your multi-canvas mockups can now be used as click through prototypes in Acrobat. Download the demo PDF file for a test drive.
http://www.balsamiq.com/blog/2009/11/13/weekly-release-export-to-pdf-a-fresh-coat-of-paint/