Input and Output pin voltage specs on a datasheet
On page 38 of the datasheet you'll see for instance that the voltage on the PB should never exceed Vcc + 0.3 V. You'll find that this is true for almost all inputs on ICs: the input levels should remain between the rails. An exception is when you have for instance 5 V tolerant inputs on a 3.3 V powered microcontroller, but then that will be clearly indicated in the datasheet. (The manufacturer will consider this as an important feature, so he will make sure you notice that.)

To know if the high output will damage the input of another IC with a Vcc of 2.7 V you'll have to consult the datasheet of that IC. Probably the same limits will apply: input voltage should be no higher than the 2.7 V supply.