Are there any concrete documents or plans that show Paizo (the Pathfinder publishers) are planning to move to D&D 5e?
No. Not at the time of this answer.
Paizo and WotC are not the same company. Back when D&D 4th edition was released, Paizo chose to stop supporting D&D, instead releasing their system as a standalone OGL modified from the 3.5e rules. In effect, Pathfinder is its own independent game which happens to have its roots in an older edition of another game. Since there was no jump to 4th edition, it is unreasonable to expect a jump to 5th, especially as no such commentary has come out of the publishers, unlike what happened when 4th was released.