To install at minimum you’ll need to likely shrink existing partitions and create new ones for linux if you don’t want to wipe the drive, that would be a dual-boot setup with Windows still installed along side. Or you can just wipe the drive entirely and have only Linux.
Regarding the files you should already have backups of anything important, if you don’t, set it up ASAP.
Messing with partitions can easily cause data loss if something goes wrong.
You also never know when hardware failure, malware, power surges, lightning strikes, or whatever other disaster will happen and cause data loss. 1 copy of files might as well be 0 copies.