You can save a text file into the resources - it's easy, and I do it with every project for revision history purposes.
But...you can't easily put a different text file into each installation of the assembly, not without rebuilding the application for each separate installation. That's messy, and dangerous - because you can easily end up with changes going out that you don't know about.
Instead, create the licence file and store it in a "sensible place" - don't try to make it a part of the EXE file.
Where should I store my data?[
^] may help - and if you use the application GUID as part of the path, it won't be easy to find.