I don't see a MIDI connector on the Play Acoustic but can I use a keyboard with this device?
Yes, the Play Acoustic can also be used with a keyboard to trigger it's harmonies. In this case you'll want to plug the keyboard output into the 'guitar in' and use the 'guitar DI' to pass on your signal from the keyboard to your amp/PA. In some cases you'll require a line transformer to help with this.
In order to get the an un altered sound from your keyboard select the 'Guitar FX' tab. Turn down the level on the "Guitar Reverb 1/4' and 'Guitar uMod 2/4'. Under 'Bodyrez EQ 3/4' set it to flat, low and hi gain should be set to 0. Under 'Guitar Anti-Feedback 4/4' Phase invert should be off, Lowcut - 20 hz, Notch gain - 0db.
Keep in mind, sounds with definite attack like piano, harpsichord pizzicato strings may work better for triggering the harmony. Sounds with a long soft attack like bowed strings or pads may not do the best job.