The class libraries that come with the JRE have no provisions for creating PDFs. Check out iText, which is the premier open source library to create PDFs. Its 2.x versions run under Java 1.4, while the 5.x versions requires Java 5.
Why are third party libraries not allowed? Is it because of licensing? Because yes, iText's licensing (AGPL) can be a reason to not use it.
Nothing prevents you from rewriting something similar from scratch, but you should tell your project manager that that will require several months of extra work. Perhaps purchasing a commercial library is cheaper.