What is the word for something I am reading that is difficult to understand, maybe purposefully so? I would prefer an adjective.
There are several possibilities, but I would go with abstruse.
An adjective describing complex, impenetrable text. It can be applied to both deliberately obfuscated text and to badly written verbiage.
If someone were to purposefully write something so to make it difficult to understand, they may be obfuscating the passage. (Obfuscate at Merriam-Webster)
Cryptic is an option. It can be used to describe not only text that is difficult to understand but also text that may be purposefully obscure.
difficult to understand : having or seeming to have a hidden meaning
"Although I enjoyed much of his earlier work, I did at times find it hard to make sense of his cryptic ramblings."
You could use the word opaque. This doesn't quite address whether it was written this way purposely, however. Some of the other suggestions here propose words that suggest multiple, hidden, or ambiguous meanings, while this one indicates text so difficult to comprehend that it's hard to extract any meaning.
opaque - (especially of language) hard or impossible to understand; unfathomable.