PNM Viewer is a simple Java utility for interactively viewing and editing PNM text files. It's available free of charge.
Right now, there isn't any documentation about PNM Viewer. To use it, you'll need Java 1.2 or later installed on your computer. Then you can download pnmviewer.jar.
To run it, you might be able to double-click on the file. If that doesn't work, execute java -jar pnmviewer.jar at a command line.
If you find PNM Viewer useful, let me know!