Moving this discussion to the RoboHelp forum.
Contact Adobe Support and explain your situation. Make sure you have your purchase paperwork. They can activate you over the phone. They do this for places like defense contractors and the like with FrameMaker all the time.
Welcome to Adobe Robohelp forums
The question itself answers the question. If you use trial of any Adobe Product it means you do not have the serial number of Adobe product to activate.
So activation comes into picture for any product when you have license/serial number of that product. For trial version you can act like a boss even if you do not have an internet connection because you need not to worry about activating the license key/serial number of that product.
Hope it helps
@VJ I believe, he owns a Serial Number, and is unable to license his product as it might be asking for Internet Connection as per the process. I might be wrong, this could also be a possible scenario.
@ Sam, If I understood you right, can you let us know you Rh version. If possible share me the details (Adobe Order Number/ Serial Number) via private message. Based upon that, I can suggest you about something.
Else, VJ is right if you do not own the Serial Key.