Digital Output Voltage

If i am powering a 12 volt motor from a digital output, do i need a 12 volt power supply connected to the output module.

http://accautomation.ca/how-plc-outputs-work/

http://accautomation.ca/programming/plc-basics/

This will depend on specifically what the digital out is that you have.
If you have a relay then the output needs to be powered as you suggested with a 12V power supply.
Check the specifications of the PLC that you are using to determine the kind of output and the amount of voltage/current it can handle. Do the same with the device that you are trying to control.
If you are trying to switch too much then an interposing device is required. This can be a relay or SSR usually.

Hope this helps you out.
Regards,

That really depends on if it is digital or a relay out.

If it is a relay out, then you can use your 12V power supply as the common for that section of outputs. If your output is a digital output, then you will want to use an interposing relay to turn on this motor.

You really don't want to run an inductive load from a PLC digital output.