The open specification allowed the development of all kinds of open source tools (as well as closed-source tools) that make PDF much more useful to everyone, yet Adobe is protected from having its development investment and future business stolen.
If by having its business stolen you mean having to compete on the stre[n]gth of its products in a free market.
What I mean by "having its business stolen" is having someone else market or give away the idea that has cost the firm or individual(s) time and trouble to develop.
Take Robert Kearns, who invented the windshield wiper delay, for example. He came up with the idea of how to solve an annoyance that most of us experience from time to time. He went to the considerable time and expense of developing, perfecting, and patenting his idea, then approached the large auto manufacturers, asking them if they'd like to license his patent. They rebuffed him and proceeded to use his invention to make millions of dollars. It took him decades to get any compensation for his initial R&D. As far as competing on the strength of his products in a "free market", he could hardly have been able to start his own automobile manufacturer so he could sell his invention; would you argue, however, that Detroit was entitled to make money from his idea without compensating him?