That's super simple.
There are many more talented people out in the world who can (and will) create fantastic creations using PACG for free than Paizo could ever hope to hire.
* Release the tools to make it easy for them to do so.
* Release an "API" - or published quality and standards document.
* Provide a way for players to submit works to be considered for official publication.
* Actually consider those works.
* Publish the best of them as Official Releases.
* Compensate the designer with something (1st published set, and a small royalty per set sold would probably be *far* more than someone who built the set out of the love for the game would ever expect.)
The success of a product like PACG hangs, I think, more-than-a-little on the sheer amount of quality content available for it.
Start with "Create a character in Pathfinder RPG, use this conversion template/process, print this two sided PDF on this recommended heavy cardstock. Play PACG with YOUR character."