Adobe Acrobat has done a tremendous job to make sure their Reader could read and display any kind of pdf, mostly incorrectly built pdf that don't respect the agreed format. The downside is that it allows vendors to produce non-standard compliant pdf. In other words, the hard work from Reader team encourage vendors to make **** ! And there's no way one can deal with that by using a truely free ISO compliant library.
If PDF can only be read by one application, PDF is not a portable document format anymore. Adobe destroyed what they had built