Thanks for the reply, and sorry for the long delay in trying this. The above worked perfectly, once I figured it out that I had to go to the “File Sharing” section instead of just selecting the first NoMachine icon presented in iTunes. I would simply clarify the instructions as follows, at least for those connecting the iOS device to a Mac through iTunes:
Open iTunes, select your device, click on the Apps item on the left, then navigate to the “File Sharing” section at the bottom of the page. Select the NoMachine icon, then click the `Add…’ button. Navigate to the location of your key file and select. This will add the file to the file structure on the iPad. (I found mine under the Documents folder that was offered when I browsed the file system as described above.)