@OmnipotentEntity makes a good point. Most (and definitely older) laptops have 1 drive. Which would mean your C and D ‘drives’ are actually 2 partitions on 1 physical hard drive. This is fine, but you need to be extra cautious when installing Linux. Many linux installers push you to the easiest choice and select ‘wipe whole disk and install linux’, which in your case would possibly lead to inadvertently wiping the D partition too.

You might want to pay extra attention to this during the installation, when selecting which disk to use for installation. Make sure you only let the installer delete the C partition (which will probably not be named as such, so be ready to find another way to identify the correct partition (maybe by its size?)), and let the installer use the free space that gives to create linux partitions it needs there (next to the D partition).

NB: Still in Windows, you may also want to check whether or not your D drive is encrypted with Bitlocker, as that is a Windows-type encryption and cant be unlocked without a recovery key (aside from it not being practical to use Bitlocker encryption in combination with linux (or NTFS for that sake, as OmnipotentEntity also already mentioned)). If so, you might want to decrypt the D partition so you can still access it from Linux (while it is of course better to have encryption enabled, it may be a temporary convenience).

Edit: Solid choice of Linux Mint btw. It’s been a while since I’ve used it, but in my memory (also as a starting Linux user) it made the right things easy. If your laptop is quite old, and Cinnamon (also solid) doesn’t feel quite snappy enough, you could give XFCE a try. It’s less polished (some say ugly 😆) out-of-the-box, but also less resource hungry (Cinnamon and XFCE are both Desktop Environments (DE’s). On Linux you can have multiple DE’s installed side-by-side; and then make a choice which DE you want to use when you login)