The first thing you should always remember about any study guide is: they are only as good as the person using them. This means that no study guide can help 100% of its readers pass the Basic CCNA exams. At the most, study guides can help a lot of people but there has yet to be made a study guide that can claim 100% passing rate for all its users.
Secondly, a PDF file is usually used by Basic CCNA Study Guide creators who want to be sure that their material will not be copy-pasted into another electronic document. It depends on what security features the PDF file has but generally, all PDF files are supposed to be secure from tampering – which is why the PDF program is used even for government documents to assure security risk is minimized.
When studying, it is very important not to race through the questions. Yes, there may be a prescribed time limit (you could invest in a stopwatch so you can time yourself) but if you budget your time well, you may find that you have time to answer most of the questions. Do not panic. You probably know the answers to most of the questions but panicking will cause you to have a mind block.
If you find yourself panicking, breathe deeply and look into the far distance. Try to relax then go back to the questions.
Prayer never hurts (before, during and after the study session.) You never know if God might be listening.