Update follow pdf version 2.0

[3xploiton3]

ISO published version 2.0 of PDF, ISO 32000-2 in 2017

https://en.wikipedia.org/wiki/PDF

[maxpmaxp]

@3xploiton3 PDF 2.0 is largely compatible with PDF 1.7, do you have any samples you can share that make pdfreader fails? Or provide any PDF2,0 specific features to support?