Downloading a pirated version from the murkier parts of the internet is illegal, and it’s also a big risk for the security of your devices and data. Taking out a trial is the only legit way to download InDesign for free.
If you don’t cancel, Adobe will start to bill you for a subscription, so keep your eye on the calendar if you decide you don't want to continue with the software.
You’ll have to provide your credit card details to start the trial, but if you cancel your subscription before the end of the trial, you won’t be charged a penny.