Teacher put all of the answers to the homework in white font?
There are several reasons you should do the work yourself, ignoring the filled in answers:


It is the honest thing to do.
You will learn far more from the homework that way.
The filled-in answers may not be the right answers. For example, the teacher could have used a file from someone who had done the homework for calibration, and made some mistakes.
If the teacher sees a lot of 100% correct answers, with exactly the same wording and formatting, they may become suspicious and realize what was going on. In that case, it may be very important to be able to honestly say you did the work yourself.