You may want to watch this [YouTube video][1] - it shows the scenario that I believe you're looking to solve - it uses Preview to create a multi-page PDF.

The steps are:

 1. Open your images in Preview
 2. Select `Print` from the `File` menu (or <kbd>⌘</kbd><kbd>P</kbd>)
 3. Click on the "`PDF`" button in the Print dialog and select "`Save as PDF...`" from the dropdown
 4. Provide a file name and `Save`

  [1]: http://www.youtube.com/watch?v=Z0ZyHLSMr7g