The guide above assumes that you have an author license (and a SNAP license, for some of the example code). If you do not have an author license, you cannot add a reference to the Excel library, but you can still effectively work with Excel (it's just more difficult).
Here are a few examples of working with Excel with no license (searching may turn up more):
If you use the example code from nxjournaling, I'd suggest adding in the "cleanup" code provided by Yamada; not all of the examples include it. Also, check the NXOpen samples folder that ships with NX; there is at least 1 example that uses Excel.