Ransomware is a growing problem. It infects PCs, encrypts your files, and holds everything hostage until you pay a ransom - hence the name. The best defense against ransomware is frequent backups and strong security software, but Windows 10 now includes basic protection right in your operating system.
Controlled Folder Access protects your files and folders from unauthorized changes by unfriendly applications. Your Documents, Pictures, Movies, and Desktop folders are protected by default, though you can block other folders manually or whitelist trusted software to access your locked-down info.
You can tweak Controlled Folder Access by going to the Windows Defender Security Center, selecting 'Virus & threat protection', then selecting 'Virus and threat protection settings'. Scroll down to 'Controlled folder access, and turn it on if it not already.