PC-Mac external drive partition?

I have a western digital external hard drive that I backed up my previous PC on. Now I have transitioned into a macbook and want to back up using the same external hard drive as I have a lot of space left. Can I partition the external drive and separate out the PC section and reformat a section to back-up my Mac? Or would I have to erase the hard drive, partition it, and then re-back up both computers? I’ve had a hard time finding info on how to do this on the Western Digital website, beyond how to partition the drive before you save anything on it.