You will need SCJP 5 books if you are planning to take the SCJP 5.0 exam version. SCJP stands for Sun Certified Java Programmer accreditation and SCJP 5.0 is one type of accreditation exam for that.
If you have extensive Java coding experience, then you have a leg up on people who are fresh initiates into the Java language coding experience. For those newcomers, they may find the SCJP 1.5 book by Kathy Sierra and Bert Bates to be quite helpful.
The SCJP 5.0 exam itself is formally called The Sun Certified Programmer for Java 2 Platform 5.0 certification exam. It is not meant for novices rather it was designed for accreditation of Java programmers who know this programming language quite well and have used it for some time.
The SCJP 5.0 exam tests the Java programmer as far as his knowledge of the fundamental Java programming syntax and programming structure are concerned. To prove this capability, the Java programmer has to be able to produce actual functional Java applications whose technology relies on desktop and server systems based on J2SE 5.0.
Actually, there are two versions of the exam to test J2SE 5.0 knowledge. For IT people who were previously certified upon passing the SCJP 1.4 exam version, they need only take SCJP: CX-310-056 which will upgrade their SCJP accreditation. They are allowed to simply upgrade their accreditation status because Sun assumes they already comprehend the basics of J2SE 5.0 knowledge and skills. Those who come freshly trained in J2SE 5.0 but lack any experience in real coding of Java will have to go take the full exam (dubbed SCJP: CX-310-055.)
First, you need to understand that the PDF document format from Adobe is one of the most secure means for creating documents lately. A SCJP certification study guide that is in PDF document format has security features that prevent easy copying of the data (especially if it is original or unique data that the authors would like to protect.)
With the Adobe Acrobat 8 Professional software, an authorized end user can be granted unique passwords so that the originator of the SCJP certification study guide can control who gains access to his data. Without the necessary passwords, the end user may lack the capacity to do certain functions like print out the document, make changes to it, or even just open and view it.
If you are talking about free SCJP Certification study guides, these are probably open source materials because they come at no charge to the end user. But the problem with open source materials is that not everyone will respect the right of the original author to see that his original materials stay the same that is why the original author of such open source materials may need to rely on the PDF document format from Adobe to contain and protect his data from people who might alter it or corrupt it.
Even government agencies trust the Adobe PDF software for protecting the integrity of their sensitive documents. So if you come across any SCJP Certification free PDF format study guides, make sure you get authority from the study guide author to use these PDF documents first.