GetFileUrl method is removed from Kentico 11 and 12. Please check the below URLs
1. https://devnet.kentico.com/documentation/api-changes/kentico-12/26046
2. https://devnet.kentico.com/documentation/api-changes/kentico-11/24985
Refer below URL, how to use GetAttachmentUrlByGUID method
https://docs.kentico.com/k12/developing-websites/loading-and-displaying-data-on-websites/writing-transformations/reference-transformation-methods