While PDF is supposed to be an open standard I'm noticing more and more functionality in PDF files that isn't supported by readers who implement the open standa

While PDF is supposed to be an open standard I'm noticing more and more functionality in PDF files that isn't supported by readers who implement the open standard. I have project right now to find out why Adobe and Chrome are so different and, though it's obvious to me, the loss of functionality because Chrome doesn't support certain things must be explained to those to whom it is not so obvious.