Amazing share on the tooling side of thing for PDF processing.

More on PDF and why it's hard to do analysis [1]. TL;DR

     "PDF was never really designed as a data input format, 
      but rather, it was designed as an output format 
      giving fine grained control over the resulting document."

By the way, the PDF 1.4 (most widely used version) specification is over 1000 pages![2] To make it even harder, not everybody follow the spec :)

[1] https://news.ycombinator.com/item?id=33146364

[2] https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandard...