The answer here is, it depends on what your goal is and how you want to set things up. Is it possible to have more than 1 URL associated with a feature class in ArcMap? Sure, just add multiple attribute fields to the feature class for each URL. You can then identify the feature and click on the desired URL.
If you want to use the Hyperlink functionality in ArcMap then yes you would be limited to one field and one URL per field. Some more information on Hyperlinks below:
But if you give us some more information on what your end goal is here, we may be able to provide a way to do it.
Thank you very much for your reply. It's a good idea to have another fields for additional URL's, but I cannot foresee the number of possible linked documents. So, it'd be nice if we can just link any number of URL's in one field without much scripting or programming.