Patellofemoral pain is often not a symptom of damage to the knee, but of tight quadriceps muscles. SMR can provide quick, effective relief.
With all the "running hurts your knees" propaganda that gets spread by people who either know no better, or have an interest in promoting alternative cardiovascular training options, it's no surprise that any knee pain following running is interpreted as injury to the knees from running.
When your quadriceps get tight from running in a quad-dominant manner, rather than the more natural way of running, where the glutes are the major driver, patellofemoral pain is almost to be expected.
A quick solution is to use self myofascial release (SMR) to improve the tissue quality of the quadriceps muscles.
My favourite approach is the use of a lacrosse ball (or similar) placed in the supra-patellar pocket and used to pin the muscle in place as you pull past the pinned spot. This works very well acutely in most cases to relieve the pressure on the kneecap.
A slightly longer term approach is to use the foam roller to find tight bands in the quad muscles and to clear them up, either using a simple pressure release techniques or a similar "pin and pull" approach to that used with the lacrosse ball.