First make sure you installed the JDK using its setup program as it writes important information to the registry that TextPad needs to locate Javac.exe. If you copied the JDK from another machine it will not work correctly with TextPad. After you have run the installation program for the JDK, do the following:
1. Click on Configure.
2. Select Preferences.
3. Select Tools.
4. Delete the 3 JDK commands (if present).
5. Click Apply.
6. Click the Add button and select the JDK commands.
7. Click OK.