When you launch a file, by selecting it in one of the panels of AB Commander, and pressing Enter (or double-clicking it), normally AB Commander launches it by passing it on to Windows, letting it open the selected file with whatever application is set up to handle the files of that type. Usually this is exactly what is supposed to happen, but what if you want a different application to open the files of a specific type? For example, you could have more than one text editor, and you want a non-default text editor to handle text files when you launch them from AB Commander, while still being able to open them with the default text editor from File Explorer?
To facilitate such a possibility, AB Commander offers a way to set up an unlimited number of custom launchers. Each such launcher would specify which file types it should apply to, and which application to use to handle the files, when you launch them from AB Commander.
Press the Custom Launchers command and another screen should open displaying the list of the custom launchers you had previously set up. (Of course, if you had not set up a custom launcher yet, the list would be empty.)
To add a custom launcher, press the Add button and specify the file name extensions this launcher should be used with, as well as the application and the command line arguments to pass on to the application:
After you have set up one (or more) custom launcher, whenever you launch a file, AB Commander would check the file name extension (such as .txt or .pdf) and see if there is a custom launcher for it. If you have not set up a custom launcher for the files of that type, AB Commander will ask Windows to open the file, as usual. However, if it finds a custom launcher, it starts the application you have specified and passes to it the command line arguments you had specified as well, replacing the placeholder %1 with the actual path of the file you are launching.
Note that if at a particular moment you don't want to use a custom launcher to open a file, press the Shift key while launching the file, and that would make AB Commander pass the file on to Windows directly, as if no custom launchers were set up. This gives you the flexibility of choosing to use or not to use the custom launchers, depending on the situation. Note also that you can flip the meaning of the Shift key in this context, by selecting the appropriate option.