Question: I'm getting crazy, cause I cannot find what are the "default" keys you would have in a PDF Document.

For example, if I want to retrieve an hyperlink from a CGPDFDocument, I do this:

```
CGPDFStringRef uriStringRef;
if(!CGPDFDictionaryGetString(aDict, "URI", &uriStringRef)) {
    break;
}

```

In this case, the key is "URI". Is there a document explaining what are the keys of a CGPDFDictionary?

Answer: 
The [Adobe PDF Reference](http://www.adobe.com/devnet/pdf/pdf_reference_archive.html) describes all of the keys.
The keys in a dictionary depend on the actual object the dictionary represents (a page dictionary has other keys than an annotation dictionary). The Adobe PDF reference describes all these objects and their keys.