Can I do a Time Machine backup to an external hard-drive without erasing the content that I already have in the disk?

I have an external hard drive that I am using to save my work, and is the only one I have. I would like to use it to make a Time Machine back up, but I'm afraid that doing so will erase the other data that I have. Right now the disk format is ExFAT, and I think that in order to make a Time Machine backup, I need to change it to another one.

Thanks!