Whether or not the text of the PDF is 'available' is an option for the PDF publisher. I remember several tech documents that were designed intentionally to not allow you to copy the text out of them.

It sounds as if your target document might fall into that category. You could check by using a 'normal' browser to save the file to disk. Then open the file with an 'official' reader and check the properties.

(This would also give you a pdf on disk that you could practice the pdf part of your code with.)