These puzzles are in Portable Document Format (PDF). They require Adobe Reader which is available free from Adobe:
The puzzles are specifically formatted for printing. They may not look good on the screen, but they should look nice when printed. Also note that the files are relatively large (around 400 KB each) and may take some time to load completely.
If you get stuck on a puzzle and need a hint, go to the interactive version of the puzzle and use the Hint button.