Hey,
Seto ransomware is one of many malicious programs that belong to the Djvu family. These programs are designed to encrypt files and block access to them. To regain access, victims are encouraged to purchase a decryption tool from cybercriminals. Seto renames all encrypted files by adding the ".seto" extension to the filenames. For example, "sample.jpg" becomes "sample.jpg.seto".
I would suggest you click here https://www.pcrisk.com/removal-guides/15761-seto-ransomware to get the steps on how you can retrieve your files.