How do I run a script on a .indb file?

I do this like so:

var inddFiles = GetFilesFromBook();
for (var i = 0; i < inddFiles.length; i++) {
    inddFile = inddFiles;
    app.scriptPreferences.userInteractionLevel = UserInteractionLevels.NEVER_INTERACT;
    doc = app.open(inddFile);
    app.scriptPreferences.userInteractionLevel = UserInteractionLevels.INTERACT_WITH_ALL;
    // Process document
    doc.close(SaveOptions.YES);
}
function GetFilesFromBook() {
    var bookContent, file,
    activeBook = app.activeBook,
    files = [];
    
    for (var i = 0; i < activeBook.bookContents.length; i++) {
        bookContent = activeBook.bookContents;
        if (bookContent.status != BookContentStatus.MISSING_DOCUMENT) {
            file = new File(bookContent.fullName);
            files.push(file);
        }
    }
    
    return files;
}

Here is the whole script that you can use as example.

Documents in a book are objects of type bookContents. Open a document, process it, and save/close it. Do that with all book documents.

Peter