It is possible to associate TreePad Lite with TreePad .hjt files. When TreePad Lite is associated with .hjt files, you can double click on a .hjt file (in Windows) and TreePad will automatically start and load that file.
To perform the file association, you only need to click
"Menu: Tools/TreePad .hjt files/Associate TreePad Lite with .hjt files"
This tells Windows that from now on TreePad Lite is the default program to open TreePad .hjt files.
After this, you can double-click on a TreePad .hjt file (in e.g. the Windows Explorer file manager), and Windows will know that TreePad Lite needs to be started to open it.
To do the reverse, i.e. to remove the file association with TreePad Lite, simply click
"Menu: Tools/TreePad .hjt files/Remove file association"