They don't have to now. They can use one of the freeware clones, or heaven forbid download a free reader direct from MS.
What operating system is required to run the free reader, who sells it, and how much does it cost?
90% of their constituents already have access to it. Those that don't, know someone who has it, or can easily access it at a library or rent time at countless locations without even being required to own a computer.