If you want to create a Hello World file in PDF, you need a library to do so.
For instance: this Java HelloWorld example creates this hello.pdf. Download hello.pdf and open it in a text editor, and you'll see that it contains much more than the bytes "Hello World".
I see that you're a C# programmer. You can find the C# port of the HelloWorld example here. iText is only one of the many libraries, I'm mentioning it because I'm the original developer of iText. A simple search for PDF libraries will reveal more options.